The bellhousing change you remember was likely to keep the correct mounts for 48-53. Starting 54 they changed and your newer engine probably had the newer housing.
My GMC 1 ton with just an old worn 228 would go about 45-50, and once in 4th gear it would pull even reasonable hills at speed, very little shifting once cruising. Same with my 52 with the 235 years ago. Both had 5.14 axle gears.
I'm a little surprised your truck with even lower axle gears than mine won't pull hills very well. Understandably it won't be fast, but should hold its speed once you get there. This all unloaded, with a load they'll slow down for sure.
Was it running well in your opinion?
Grigg
