Help me out guys, looking at putting in a new transmission.

[3/4ton72heavychevy]

As the title says, this 4 speed is not doing it for me. For not being uber powerful it sure does suck gas, and my clutch is needing replacing anyways so I have thought of redoing it all but am not sure what different transmissions will work.

It is a 1972 chevy C20, 350, sm465 4 speed granny gear.
What different transmissions will bolt up with minimal changes?
Auto and manual welcome.

[SS Tim]

The trans is not the problem. Your truck would have come stock with 4.10 gears or the optional 4.56. If both power and mpg are down then it might be the carb that needs attention probably timing too. Once you have the engine up to spec then you can decide if the truck is geared too low for your normal useage. A 3.54 axle from a big block would be pretty close to bolt in more so if you have leaf springs and the Dana axle.