Not sure about the electic suspension, but it's fully loaded and has the auto-leveling rear. The ride is great on the road, very smooth. I only notice the recoil thing on speed bumps.
I'm getting about 13.5 mpg towing or not (I have a lead foot when I drive without the boat, so that's why it's about the same mpg). I have a '03 Chevy 2500HD with the 6L Vortec, and it get's 12 mpg and it's not even full time 4WD like the Denali. I was actually suprised that I got 13.5 mpg in the Denali when I first got it, cause I was driving it really hard. By the way, Hawaii uses gas blended with 10% ethenol, so the mpg is probably 15% less than what it would be with pure gas (ethenol was supposed to cut our dependence on foreign oil, but in reality the cars use more gas than before, but the politicians think they are doing the right thing