So, just had the first opportunity to tow with the new '08 (1,600 miles on the odo). The "old" truck was an '04 6.0 (both are crew cab, long box, 3.73 gears)... and the 5th wheel camper weighs in right around 12k loaded.

By comparison, the 6.4 doesnt seem to pull quite as effortlessly as the 6.0 did. I experienced considerably more TC lock and unlock in the new truck on roads where the 6.0 would maintain speed in 5th gear with the TC locked.

To give an example -- with the old 6.0, on the 2 hour trip down I-76 to Denver it might unlock the torque converter once or twice at 65mph (maybe double that in a heavy head-wind) and always maintained speed within 2-3 mph. The new 6.4 probably unlocked 30 times and would drop 5-6 mph off of the cruise setting.

At 65 mph in the old truck, if I would start to pull a steep grade the TC would unlock and then it would shift down to 4th gear. In the new truck, even floor-boarded, it wont shift into 4th gear at anything more than about 59 mph... which means that at 65 mph I can get a max RPM of only about 2,500 even under full acceleration -- and in the mountains it wouldnt maintain speed like the old truck would. Between Colorado Springs and Canon City there are a couple steep climbs that the 6.0 would hold 65mph in 4th gear but the new truck would only hold about 56-57mph under full acceleration.

I'm wondering if anybody else has noticed anything similar if you've been able to compare the two engines under the same load on the same roads?

According to my Oasis report, the truck has the latest programming.

Thoughts?

 

Well,

I have towed considerable with mine and mine does not lug anything like what you are decribing.

I have done up 80 pulling 6/7% grades pulling around 10K. RPMs around 3K. I have 15K on my truck now. At 80 mpg I was also pulling close to 40 lbs of boost.

 

I have A F450 with the 6.4 motor, I feel the trans isn't down shifting or coverter unlocking. Like you my old truck with the 6.0 motor would pull the same trailer up A hill A lot faster.

 

Our 09 6.4l has a break in period of 7500 miles @ 75% max output built into the computer, I was told it worked for speed and towing until 7501 miles then it would let you go.
Maybe this could be your computor trying to keep the engine in break in mode?

 

Interesting notion. Anybody have more info on this?!?

Thanks for the responses!
Mike

 

The problem with this idea, is mine dose the samething with 13,000 miles on it.

 

I had 2 6.0's and now this 6.4. I dont feel feel much (if any) difference in power but the 6.4 truck is also heavier than a 6.0 truck. I also think that the computer programming for the emissions (specifically the accelerator delay) make it feel even less powerful. I noticed on my 6.0 when I went to pass and would "floor it" that the engine would rev up and go. The 6.4 feels like it downshifts 1 step instead of 2 because when you floor it the rpms dont jump as high and it doesnt seem to have as much pick up and go (I even took my floor mat out thinking I wasnt getting full pedal).

But again, its a heavier truck and its programmed differently to reduce soot output.

 

I don't think it's a motor problem, It seems like the trany down shifts out of fithe gear to easy then dosen't unlock the converter when needed. I pull a 7000 pound trailer and when I go up a steep grade @ 60 mph the rpm's are holding at 2600, on my 6.0 the converter would unlock,and the rpm's would jump to 3500 and pickup speed.

 

Exactly what I was "trying" to say but you said it better. I dont think there is anything wrong but its different and the seat of the pants doesnt feel/sound/look like its got any more guts than the 6.0.

 

I never got to drive a 6.0 but I am not surprised that you all find the 6.4 to be a bit of a let down. The thing is a strange motor with all the emissions control on it. It has that 2 stage turbo thing which is questionable on whether it works or not. It has like 8 radiators, even cools the diesel fuel before it gets burned.

I really like mine, drive it hard and long every week. (make your own jokes please)

For me, the 6.4 is a dream after driving a '05 Duramax. So much smoother, quieter, and easier to drive smoothly.

 

I too have never driven the 6.0 or I might know more of what you are saying here. Before this all my experience with disels is the heavy stuff when I was in the Army.

But I really dont think my 6.4 acts like is has been described here. Now when pulling grades it will maintain the speed with the boost coming on, unless it is really steep then it will downshift as required.

 

I have pulled with both. The 6.0 Solo would blast pass my 6.4. Towing the 6.4 will walk past the 6.0, but the mileage is less. I towed a 35' fiver with both trucks. There is a pretty good grade coming out of Gorham NH headed towards Lancaster. Coming into the hill you have a 35mph limit. Once into the grade it changes to 55. The 6.0 would top at 57-58 right on the carpet in fourth, the 6.4 was doing 65 in direct with a little more if I needed it. The 6.0 would get about 13mpg on this trip and the 6.4 gets 9-10mpg.

 

I have yet to hook my 08 350 up to my 5er but will at the end of the month. My 05 would groan a bit but once we were going no problems. So I'm very anxious to pull. I have just about 3700 on it right now so by the end of the month should have 4k and ready to pull.

 

Dont forgot to post back cause i'm curious as well to your findings.

 

Well, I will chime in here as well. Having on 04, job 2 truck with turbo back exhaust, air-raid intake, towing an 11,000-lb camper, I definitely knew it was back there. Mileage with the 6.0 was about 10-11 depending on speed. I think the 6.4 tows the camper better and seems a bit more responsive. I kind of wish I had the 3.73's due to the weight, as I get a bit of shudder when I try and take off a bit to quick. I have another big tow coming up in a few weeks and will give an updated report then as well.