Poor fuel mileage - 86 K10

[Orion88]

I'm fully aware that nothing with the aerodynamic properties of a brick will get great fuel mileage, but with the setup I have I think I should be averaging more than 9-10mpg.

86 K10 long bed with a camper shell, stock height, 31" BFG tires, stock 3.08 gears, 350 with world products S/R heads, edelbrock performer intake and 600cfm carb, recently rebuilt 700r4 transmission, stock exhaust, has a small cam but no idea on the specs, daily driver.

Part of the problem is the quality of the fuel in Indiana. Highway driving through Kentucky last year I got up to 15mpg, which is around where I think it should be.

If all I cared about was mileage I'd just castrate myself and drive a Prius, but poor mileage in my eyes signifies something isn't performing like it should or parts are improperly matched. Knowing my cam specs would help I know. Are my 3.08 gears too high and I'm wasting all my fuel getting my truck moving? Any other thoughts/suggestions appreciated.