Ideas for best gas mileage?

[Farmstore34]

OK I know its a big heavy truck with a thirsty 350, but I need some ideas on increasing the fuel mileage. I currently average 5 to 8 MPG. Heres what I got:
'70 Chevy 3/4 ton 4x4
newer 350 V8
SM465 4 speed
I believe 4.11 gears.
I have a Carter AFB 4 barrell carb, complete MSD ignition system, dual flowmaster exhaust and an open element air cleaner. I am considering:
1. smaller carb (either 2bbl or 500-600cfm 4bbl)?
2. RV camshaft?
3. different exhaust setup?
4. changing out the axle gears (right now I can start out in 3rd without any problem).
5. Taller tires? Currently running LT265/75/16
Any ideas would be great! Thanks!!
Colby.