Just remember size does affect MPG, but not nearly as much as tire weight. Most guys don't realize that they are replacing stock 39 pound tires with large E-range 69 pound tires. That's what really kills MPG.
I've been searching the same thing, trying to find a light 34" A/T tire for my truck.
Just an FYI for anyone with stock 18s, Nitto Terra Grappler G2s come in a 295/70r18 that is 34.30" tall and only weighs 50 pounds. Also Bridgestone makes the Dueler Revo 3 A/Ts in a 295/70R18 that weighs 54...