I appreciate all your comments and thoughts and this is exactly why I started the thread, to get input from others that have done it. I haven't heard from anyone running a 6.0, 35s and 4.3 gears yet and the question I keep coming to is with my stock setup and 3.73, I was missing the power band when pulling the trailer. If I do 4.10 with the larger tire, all I will have done is bring myself back to the point I was at stock.

 

My experience is with a 7.3L PSD, but they aren't too different when it comes to the RPM band/power curve.

I have a 6" lift running 37's with 18" wheels and I have 4.30's. My speedometer is almost dead nuts on.

I agree.

Stewart

 

Comment removed, I see the older transmissions and the one I have, have the same final drive ratio, in theory we should be reving the same.

 

I was going to say something about that, but thought I'd let you do your own research on that.

Hope this sheds some more light on things for you.

 

My rig is a gasser, I have had excellent results with regearing pulling a 12k TT. I know they are completely different animals as the PSDs have only about half the RPM range of the V-10, so big gear swaps are better matches with the gassers. I hope you can come up with something that works well for your truck without having it over-rev at highway speeds. I understand the OP's frustration as the diesel guys responses have him resetting his effective ratio back to stock where he feels power is lacking while pulling. My only comment to that (and I don't mean it as a jab, seriously) is that this is the first report I've read about an owner not being satisfied with their PSD while towing, the common feedback is more to the tune of "I didn't even know it was back there!"
I feel your pain Jimbo, my Ex was a dog pulling heavy with the stock 3.73 gears, it would downshift if I ran over a shadow on the highway. My gear change transformed this dog into a horse, might not be a clydesdale but a horse non the less!

 

With gear swap on Monday, I'm leaning to the 4.3 gears even though others (through their pain) have said go back to stock by putting in 4.10s. I was a Cummins owner prior and my truck was factory geared for 4.10s and it pulled like there was nothing behind me. Having the tranny shift out of overdrive with a slight grade change on the I5 isn't something I'm happy with.

With the weight I'm towing, 60 mph is just fine by me but if I push the speed up to 70 mph I'm in the sweet spot for power. With my wife and 3 girls on board and a full load behind the truck, I'm happier with the 60mph but that puts me just below the power band.

Keep comments coming, I'm enjoying the support this community has.

 

Here's my experience. I was running 285's (tires) and my TT weighs 4000lbs. Here in AZ the slowest speed limit is 65 and it's more common to find 75mph (most doing 80mph). With the 285's I'd run between 2000-2100 rpms and would only go 70mph. Then I put on 35" tires and was excited b/c then I was able to do the 75mph speed limit at 2000rpms. The Ex would even go up hills at that speed.

Then I hooked up the trailer any my delight became utter frustration. Even with my light 4000lbs TT I can't get into overdrive on the slightest incline. I am not exaggerating, I would rev over 2500rpms just to try and get it to shift into overdrive with no luck. It sucks so bad at towing that I'm considering putting on my old 285's when we tow.

So you see my dilemma, when I don't tow 35" tires and 3.75 gears are great around here b/c I can do 75mph everywhere. But as soon as I hook up the trailer I'm stuck in the lower gear doing 60-65 and my mpg sucks.

I'm considering re-gearing but I'm also wondering if a performance chip or something would help me out at those lower rpm's when towing. Then I can have my cake and eat it too.

 

Since the first week of owning the truck and having the motor bullet proofed, I have been running an SCT Tuner with the Tow Haul mode selected and the Jake brake function selected. Even with the tow haul mode, it was still shifting out of overdrive with stock tires and 3.73. I'm hoping the re-gearing will give that extra punch I'm looking for.

I will find out in so many days.

The gears that are going in are Yukon gears; as well, the company I'm using did not stock factory Ford gears which was my first preference. From my reading, the Yukon is a good gear so I'm not expecting any quality issues.

 

I wanted to update this thread w/ more information I discovered this weekend.

With 35" tires and towing my 4000lbs TT my 7.3 was a dog. It wouldn't shift into overdrive on the slightest incline. Well I have a SuperChips programmer that I suspect is at least 14 years old but you can tell the difference when you reprogram ECU with it. The programmer offers 2 modes, Tow Safe and Hi Performance. I have no idea what the difference is but the Hi Performance is definitely more power than the Tow Safe and the Tow Safe is more power than stock.

On Saturday I spent 4 hours driving up and down hills with my TT comparing the two programs. Even with the Tow Safe program I can get into overdrive on hills I couldn't in stock mode. With the Hi Performance mode it's even better, I could actually pass some cars.

What I don't know is what about the Hi Performance program causes the packaging to warn you not to tow over 4000lbs with it. Does anyone know? Right now I'm using the scan gauge to monitor boost, Oil Temp, Coolant Temp, and Tranny Temp. I have the 6.0 cooler and my Temp never got over 145 during this test. But it was only 60 degrees out. I plan on getting an EGT gauge soon.

So my question is, can I run the Hi Performance tune while towing as long as my temperatures all stay in the safe range? Or is my tranny going to give up doing this?

 

Good timing to see this thread bumped. I wanted to give an update after having the gears swapped to 4.3 one week ago.

Prior to driving the truck away from the gear shop I used my SCT tuner and updated the gear ratio to 4.3 to ensure the computer would be doing shifts at the right points now. Once I left the shop I didn't notice an immediate get up and go difference with the truck; however after 1 week I can now feel the difference on the up shifts and taking off the line. I would not say it is night and day difference but I can tell I need to use less throttle to get the truck up and going. So in short the around town driving seems easier on this big truck.

As per highway driving, this is where I worried the most after reading the earlier posts on other people's trials and tribulations. At 60mph, the truck is right around 2000rpm (maybe a hair under in the 1900s) and she purrs right along. I did several highway tests yesterday afternoon accelerating from 60mph to 70mph+ and there feels like there is tons of power. I do not feel that accelerating at speed she is outside her power band as mentioned by a different member. I would not say if you want to drive at 80mph that 4.3s are for you. Your rpms will be rather high and consuming allot of fuel.

My target speed for this truck is 60mph with a trailer on board and I'm very excited to get the trailer hooked up; however my trailer is under wraps till March so I will need to wait. The highest posted speed in BC and Washington is 70mph and at 70mph I believe the truck is just fine and I don't really desire to push the beast beyond that.

So in short I'm pleased with around town driving and highway driving with 4.3 gears, 35" tires and an SCT tuner set for Tow Haul mode (65hp bump). Once I get a full tank of fuel through the truck I will report on mpg.

Thanks everyone for contributing to my thread and from my high-level overview of this, picking gears to change will depend on how fast you want to drive these trucks. 60-70mph (weighting more to the 60 side), 4.3 work and leaves enough room to accelerate under power from 60-70+mph.

 

Thanks for the update. Here in AZ the speed limit is 75mph and I try to do just under that. So 4.10's would be my choice with my 35" tires. I worry about using the SuperChip programmer and running the engine too hot and the tranny too hard out here especially when we climb these hills when it's 106 in the summer. Do you mind me asking how much you spent on the gear swap? I'm seeing estimates in the range of $750/axle out the door.

 

Cost breakdown:
Front Yukon 4.3 gears, $275
Rear Yukon 4.3 Gears, $300
Rear 10.25 bearing kit, $250
OEM Inner and outer seals for the front (as mine were cracked and leaking), $150
Labour, $995

My truck has 173,000km and it was more out of safety I had the rear bearing s done now instead of going another 20,000km and and finding out they need to be done later so I opted to spend less now and get the bearings done.

 

Thanks for sharing. I just called a local off road shop to get a quote. I'm seriously considering doing the regear myself as I've done it before. But the quote I got for front/rear gears, bearings and seals was $1400 which isn't much more than I can get the parts for. They use dana gears and timken bearings so I can't complain. If I want the track loc serviced (my ex came w/ a limited slip) it's another $175. So I'll probably let the shop do it b/c they said the guy that does the gears has been doing it for 50 years and it's those guys you want doing gear changes not the greenhorns.

 

I do not know, but if I were to hazard a guess, I'd say it's probably because it can cause high EGT's.

I wouldn't exactly us the term "all" when you don't have an EGT gauge yet.

Stewart

 

The EGT gauge is next on the list. I just wish there was a way to hook an auxiliary sensor into the scangauge so I don't have to mount another display. Although 4.10 gears might come even sooner.