A 350 with a 2bbl carb, 4 speed granny, spicer aux. trans, 4:10 rear, 33" tires.
When me and my dad drove the truck 80 miles to Seguin, Texas we got about 10.5MPG. Right now my Dad's been driving it back and forth to work 70 miles a day(because the 700r4 in his 85 Burb took a crap, that's a whole nother story), and it's been getting almost 13MPG! That's cool with me, but I want my truck back!
The truck has a 350/400/4:10's/33" tires, but I've worn the hell out of the 33s, gonna have to put the 31's back on.