That's the Gen1 pick of the litter for US spec trucks. Very good score. Undertired, though. 31-10.50's work real nice with no mods. What year? If late 89 or later, you may also have the lockup converter a/t. Think the tranny label has an "R" code on the lockup unit. You should feel the converter lockup as you accel past 42-45mph in O/D. Won't lock in 3rd. Lockup saves 300rpms of engine speed at 3000rpm cruise.

Not responsible for advice not taken...