I too get 20 pretty consistently with a corrected speedo gear on 33's/3.31 with my 5.3/4L60E. Thats cruising steady at 60-65mph. If i go much over that the mileage drops quickly and I have keep it out of overdrive to have the RPM's in the correct range.
1985 CJ7 Project
Phase One : 5.3L Vortec/4L60E, Moser axles for AMC20, Twin Stick'd Dana300 - Completed
Phase Two: Bedliner, Rollcage, Seats, BESRK Rear Bumper w/ tire swing, Soft Top, and a few other goodies - Mostly Complete
Phase Three: Waggy 44 front, Scout D44 Rear, 4.56's, ARB's (F/R) SOA with YJ Springs, 35x12.50x15 BFG MT - Not Even Close to beginning
Also a mostly rust-free 1970 Scout 800A That I'll get to start working on someday...