I have a 1-ton with a 235 that I did the carrier swap in, and have 4.10 gears. Carl52 hit the nail on the head. Rear tire size can play a huge part. My truck runs up to about 55 mph wide open with 28" diameter tires. When it had 31.5" tires it ran probably 5 mph faster. But I can run steep hills in 4th gear alot better with the smaller diameter tires. Lower gear effect. Having said all that I am doing a T5 swap with a world-class unit from a Camaro (with an S10 tailshaft to clear the seat). This will give a lot better 1-4 shift pattern than the old 420 Muncie, which is basically a 3-speed. The OD ratio in my T5 is a .76 so that will help also.
