As i've said, i've noticed the same mileage with big 33x12.5's as with 30x9.5's because the engine speed is lower. Hills, of course i have to downshift (unless i'm above 2600RPM which means i'm doing 70mph+) and pretty much my gearing puts me at a .70:1 overdrive.
I like having my engine revving lower, even at high speeds, and it takes very little throttle at 2900RPM in 5th gear to keep momentum (i'm doing 110 on the speedo which equates to about 125-130)... and it cruises great. The same speed with stock tires, i'm at 3500RPM and it's definately using the same if not more gas. With lighter 33x9.5's i bet the mileage difference would be in my favour. I will get them for my winter set when my 30's wear out. Maybe it has more to do witht he v6.. which can tolerate lower RPM's compared to the 22re...