72 3/4 ton trans swap or no??

[troyhubers]

I have a 3/4 72 chevy longbed. 350/350. with 4.11 rearend. I am just getting her back on the road and need to know if i should put in a different transmission in the future. I will be doing some pulling with this truck. Small tractors locally. Some people have told me to get an overdrive auto transmission and it should help with MPG. I only get 11 mpg now, and i know it won't get drastically better, but woud it be worth it to switch to an overdrive auto. and if so what transmission, or should i go with a manuel. Thanks.

Troy L. Hubers