TIRES , GEARS & MPG ?

[GMC-YA]

I'm in the midst of assembling a 84 3/4 T 4x4 with a rebuilt 6.2 (n/a) with a SM465 4spd & a 2 spd aux. tranny. The axles have 3.73s in them, can any one give me any idea what mpg will be?
DUH! engine is stock, aux tranny has 20% overdrive. I normally drive with very light loads and only tow a 21' camper (aprox. 2800)
Tire size is yet to be decided, I'd like just buy them once. from what I've seen on this board I'm sure some one can help, thanks in advance!

[Craig M]

With 3.73 and 20% overdrive should be able to get 19 to 20 mpg on freeway driving at 65 mph. Mpg will get less as you drive faster or add trailer.