higher MPG

[bucktruck68]

Hi all, I'm new to the site and think its a great place to spend some time reading and viewing pix of everyone's trucks. I have a 68 Custom 10 that my dad bought brand new in 68. His first new vehicle. Before I could drive (78) he and I overhauled the engine (307) and I started sanding the body for a new paint job. That was my pride and joy by my Senior year. He gave me the truck when I graduated HS and I drove it to college and work until about 89. Since then it has pretty much been sitting. He has it at his house but I am about to bring it to mine where me and my son (11) are going to get it back up and running. My dad has done a lot of body work to it over the last few years. The engine still runs but I'm sure it will need some work. Lots to do and a lot of things going through my head on the direction I want to go so I'm using this site and everyones's experiences to help in that decision. It has 3 OTT and I'm debating whether to keep it or go to an automatic. I like the 3 OTT but I get 9 mpg and I am not sure I want my son having to deal with a manual in the amount of traffic I have around me. Sorry for the long intro but thought you guys might want to hear my background. Here's my question. What transmission/rear end combo would get me a lot better mpg than the current one? Thanks for your comments in advance.