Gas mileage 225 Slant 6

When I had my 79 d100 short bed with the slant 6, 3 on the tree manual steering and brakes and 3.55s out back// that must not have been a Monday morning or Friday night build because that thing would hit 22 mpg on a solid highway run. It would do 18-19 in mixed town/highway driving quite repeatedly. I hope I can get at least close to that with this 85. The 79 was stone stock just well maintained. This 85 is built up a little but not crazily so. .I know I'll pay a small penalty by retaining the 727 at least for now,. I may eventually either experiment with the A500 I just got (if I can find a SB trans adapter that I can afford) or else maybe convert it to a stick.