Looking for better fuel milage

really weird cuz on my built /6 (10:1/246 @ .050 cam/600DP with 66 primary jets) i got 20mpg with 3.91's @ 3500 rpm to vegas and back...

sounds you got something not working right... check all your brakes for drag parking brake cable to tight?

my 340 [email protected] 3.73 gets 15-17mph HWY going 340mile trip to fresno, no vac advance either.
Pobably gets 10-12 around town not stomping it.