I have an 85, with a 300 straight six. It's lifted up and it's geared low so when I'm in 4th gear it chugs back fuel which is opposite of what the I6 should be doing haha. If I can get that extra gear with the 5 speed transmission then I won't be at full revs going down the highway and can save myself some fuel. I can't seem to find a 5 speed for the 80-87 models but I can find some for the 88+ models. Would the 5 speed fit underneath my truck without having to cannibalize the frame and everything else? Or if not what are some alternate solutions?

 

try the Mazda M50D-R2 which was standard on the 1988-1996 with 300 (4.9) sixes. You should be able to get one from a junk yard.

 

There were 2, well 3 but ill explain.
The mazda 5spd in some trucks is an option
Also there are a wide range and narrow range zf5 trannies.

Basically what you want to find is a small block truck (4 x4 if you have 4x4) woth a 5 speed. You need to take both drive shafts, tranny and transfer, and the crossmember. You may not need it all but its nice to have if you do. Now if you have a short bed and get it from a long bed the shafts obviously wont work. You have a hydraulic clutch, these do too. It could be beneficial to take the clutch components too, mc, lines, disc and all.

All these trucks are 99% compatable from 80-96 (97 f350). You can even swap in f250/350 straight axles on these ttb front 150s. If you get a head for a fuel injected 87-96 300 it will bolt onto your engine giving you a compression boost and about 20hp boost.

Best way is to buy a whole truck thats wrecked or blown engine. Scavenge what you want, part out or scrap the rest. If you swap core supports you can also swap over the front, fenders , and hood from the newer trucks.