Best engine/transmission/gearing combination for MPG?

[Stodie78Chevy]

Okay so I have a 78 K10 right now that is currently running a small block 400 with a th350 auto tranny. I'm uncertain on the gearing. Right now I am trying to put together some ideas to make this truck get the absolute most MPG possible. My plan is to purchase a crate engine and a rebuilt tranny. So my question is, what is going to be the absolute best combination of engine/tranny/gearing or any other mods that would help gain MPG. Also I would like to stay with an auto tranny unless you think that it would make an entirely significant difference. Throw some ideas at me, it would be greatly appreciated. Thanks!

[Stodie78Chevy]

I should also add that the truck is 4 wheel drive but not full time. I have locking front hubs. Also I am riding on 31 inch all terrain tires.

[dvdswan]

well the question has been as a few times on here and answered in different was but all boil down to maintenance and driving style.

things to do:
change to synthetic oils; engine, trans, t/case, diffs - this will provide less resistance for the moving parts.
properly tune the engine
keep tires at proper inflation
keep your foot out of the throttle - buy a vacuum gauge and keep the vacuum up.
put the truck on a diet - loose any unnecessary wieght.
and the list will go on.

you also have to consider how many miles are on the drivetrain.  a fresh engine will get better mpgs than tired one.  same with the trans.  look into getting an OD trans (700R4), a lighter t/case (203s are not light by any means).

find out your gear ratio, you'll get better mpgs with 3.5s than 4.10s.  but go with what you have IMO

[Irish_Alley]

by time you replace all that stuff you will counter the little mpgs you will pick up. go to an od trans and see how far that gets you.

[Captkaos]

The absolute best drivetrain for mileage in a 4x4 would be 6.2L Diesel with a SM465 or 700R4.  You could get up to about 20mpg out of it.