If original engine which is relatively low HP than really fast gears, like 3.55, might not work out so well. You need HP to push the wind out of the way to go fast, and a little faster takes a lot more HP.
My 1 ton with original 228 and swapped 4.10 gears and 32.5" tires is geared well, drives nice, don't have to downshift to much on hills and not always looking for the missing 5th gear either. One step faster at 3.73 might just be OK on flat ground and not hauling stuff regularly but any faster than that would be a mistake.
As for a good rear to swap research and read in the forum about the GM 14 bolt from a "cab and chassis" 1 ton.
Grigg
