I've got an '06 DRW CC LB 4x4 with 4.30s and I can't seem to break 12.5 @ 65-70. I only have 8K on it so far and everyone seems to think I'll get better at 20K, but I'm not convinced yet.
I too have a '06 dually 4x4, cc with 4:11 rear and the Platnimum Edge. Believe it or not I got 22mpg on a trip. I couldn't believe it either, I would say usually though I am in the 18 range anyway.