dockrocker;1596626; said:OK, I run 35's and I am also running 4.56's. I also have the 6 speed trans. I think these trucks should have came with a bit more gearing from the factory 3.73 with the new trans. Anyway, everyone wants to say how lowering the rpm helps gas mileage, well that only works to a small degree. When I installed the 35's my rpm's fell a bunch, at 75 mph I was only turning 1700 rpm. That should equal great gas mileage according to most people on here. Well let me tell you, it doesn't. Try about 10 - 11 mpg at freeway speeds in 6th gear. ON a 3000 mile trip I experimented and pulled it back in 5th gear which brought the rpm's up to 2000 at 75 and picked up to 12 - 13 mpg. How can that be? More RPM and better mileage, exactly what most say can't happen. I took a chance (because no one recommended 4.56 with 35's) and went with MY gut feelings and boy was it the right decision. Most of my miles are not towing, lots of freeway miles and it was the perfect choice. I now get 14 - 15 on the highway, the EGT's are cooler, the trans shifts better (and its a lot easier on the trans) and the power from low or high speeds is unbelievable! Sorry for the long post, but most people giving advice have heard, or have an opinion, but haven't done it. I have and it's perfect if you have the 6 speed.
dockrocker;1596945; said:The question referred to a lifted truck with 35's. I see now he probably has the 5 speed. A 4.30 gear would put the effective gear back where he was, a 4.56 might be a little steep for a five speed but he will only be turning 150 RPM more than he was with the 3.73 and the factory pizza cutters. I do have a very good friend that has an 03 with 4.10 and the same 35's I run and it could use a touch more gear. The only way I would ever suggest staying with the 3.73 is if the cost is in the way, but you WILL save it over the long haul.
People get carried away with this <less> gear = fuel mileage thing. If you had one of these power trains in a 2wd Colorado you could probably get away with that theory. But in the real world most of us are crew cab, 4x4 and these things are like a heavy brick BEFORE we make it worse by adding a lift and larger tires. The 3.73 gear ratio was picked by GM because thats as high as you can get away with under perfect (and stock) conditions, increase the gear just a touch and I promise you it will be detrimental to fuel economy. Even with stock tires on a long grade or against a head wind, pull it back into fifth at the same throttle position and watch your speed increase.