How many MPG should I get?

[72cheysuper]

I was just looking at the mpg poll and was wondering... since I just bought my truck and really dont know. What kind of milage should I get? And what mods can I make to the truck to see a real difference? With gas prices going up faster than Mr. Bush could ever have hoped for, It is a concern.
My truck is a 72 lwb half ton, 350 4 barrel, automatic, ps, pb, air, cruise control, posi rear end (although I dont know the ratio), single exhaust. It had a complete engine overhaul 1000 miles ago and a new carb. It runs great but seems to run a little rich. Im guessing it currently gets about 13.