Fuel Economy and $4 gas...

[Kixwy2]

First, my specs:

1974 GMC 1/2 ton 2wd CA truck
GM crate 350/260ft lbs torque - stock with 1000 miles on it
rebuilt Rochester quadrajet carb
original manifold with EGR blocked off
new fuel pump, fuel lines, hoses, etc
new distributor and accessories
Timed to 11* BTDC
12 bolt rear
31" BFG All Terrains

and a ghetto dual exhaust system of unknown origin on the list to be replaced...

Ok, so I want to make sure I am getting the best gas mileage I can with this truck. I've tuned the carb so the fuel mixture is good and leaned it out some, but not enough to cause a stumble once it's warmed up. I'm not a pedal to the metal kind of driver, but it seems I'm not getting the mileage I should be. Feels like it's around 8-10 MPG, which sucks. It sounds good, and runs great, but can I get better MPG performance?

Sort of a novice at the timing/tuning thing and I'm willing to take it to a shop if it will help significantly, but also willing to try it myself.

I'm just tired of going 120 miles on a tank of gas. And paying $60 to do it.

Thoughts?