Thanks everyone for the info about my granny gear question. My next concern is that If I do any simple bolt on motor mods (exhaust, headers,carb,ect) will my acceleration be limited by the t18 trans? Also does anyone make a short shift kit for this truck? It would be great to reduce the shift stick throw. Thanks again.

 

Bolt-on engine modifications won't hurt that T-18; they are one of the toughest ones made, and area almost bullet proof.

The T-18 is a heavy duty truck hauling transmission - it is what it is. It is designed for hauling heavy loads up and down steep hills, and starting off from a stop up a steep hill with a heavy load when necessary.
I know of no transmission modifications available, as it was designed before trucks became popular as people cocoons.
Your 4th gear has the same output ratio as any other transmission (except overdrives), including the light duty three-speed - 1:1. So, changing the transmission won't get you any advantage, unless you put in an overdrive transmission.
Here are your options to reduce your high gear RPMS:
Change to an overdrive transmission - Quite difficult.
Change the rear end ratio - Easy if you have Ford 9" rear, expensive if you have a Dana.

That's about it, really. Also, if you change the rear end ratio, you lose trucking power, and will reduce the ability of the truck to work like a truck.

Good luck!

 

No short shift. It is a Truck transmission. Long and loose it the norm.

Not much can hurt it with modifications to a 352.

Garbz