Wanting to see if any one has a 5 speed 4x4 with 355s in it...... and how well you like it and what yoir seeing for mpg.... I have 411s right now with 285 after I took my lift off. ... bad part is on the highway at 70 mph iam running like 2800 to 2900 rpms.... and mpg is been17.5 and 16.... have a buddy that will help me do the gears iam out 1000.00 bucks in parts..... just wanna see if its worth it.....

 

If your towing I strongly suggest on keeping the 4.10 if your stock just keep them, unless you got the performance to back the 3.55 with

 

With stage 2 in it right now and all the work done performance isnt an issue.... also have a set of stage 3 ready to go in and swap out the 66mm for an s369. .. truck runs amazing.... just would like lower rpms and better mpg...it will still pull any thing I need to pull.... race car, 20'camper and 28' goose neck

 

Good. You have the goodies to back up 3.55, I say go for it

 

Any ideas on mpgs or how much it will lower rpms? Only chage that is going to happen is a set of 17 by 9.5 wheels and a set of 33 12.50 17 tires

 

Its hard to tell mpgs as you got a completely different setup than I do, but if I had to take a guess maybe in the 2-3mpg range

Just forget about mpgs for right know, where you will notice a big improvement is that your going to be in the power band longer in between gears as opposed to the 4.10, that there is a good enough excuse to justify the cost

 

I had 3:55 with my 5speed and 285 at 70 I ran 2 grand and I kinda miss it I now have 3:73 with my 05 axle swap and run 2 grand at about 64 mph but I'd definitely go for it might consider 3:73 though I can now take of in 2nd gear

 

As 7.3 forever said, I'm also cosidering 3.73s. I don't want to go so low as 4.10s. Currently I have 3.55s, and 35 inch tires. Starting from a stop is a royal pain in my ***, like I have to use first and I have to ease into it, but once moving she goes frickin fast. I hardly ever use 5th. I use 5th when I'm going over 110ish kms an hour. Haven't towed an thing yet, but I imagine it'd be hard on everything from the flywheel to the axle shafts.

 

^^^^^ Keep in mind that as you change diff gearing, you will see the expected change in speedo/tach relationship, but as you change tire sizes, you will NOT see that change, unless you recalibrate the speedometer. For example, I see the same 2000 RPM / 70 MPH with 3.55s that 7.3 Forever sees, even though I'm on stock tires. So with 285s (presumably they're 75 or so profile), he's actually going faster, probably closer to 73-75.

As for the break-even / payoff point, where MPG savings pays for the parts, that obviously depends on how much you drive. I suspect you won't get more than about 2 MPG improvement, or put another way, maybe 10-12%. So very roughly estimating, say you drive 10,000 miles a year, you'll save maybe 60 gallons, or about $150 (at today's prices) per year in fuel. That's a very rough guide; gotta adjust for your miles per year, etc. (as they say, YMMV).

Probably the more tangible factors are the towing factor and the "sanity" factor. As said above, higher number gears are better for towing. OTOH there's the "sanity" factor of getting the revs down at highway speed. Shoot, even with our 3.55s, I wish I could drop ours down to 1600-1700 at 70 MPH, just to quiet down the cab. So there's always a trade-off, unless you go to a double-overdrive with something like a GV. Even a ZF6 won't help you, because the range of ratios is about the same (just closer steps).