First off, power is a non issue. Plenty of power. I wouldn'y hesitate to put this thing up against my buddies 6 liter PSD with the trailers hooked up.
Second, and the thing I was most interested in is milage. Unloaded, with about a 2200 pound trailer, I averaged 13.2 mpg as indicated by the trip computer. This included having to stop at 4 toll booths, and covered a distance of about 50 miles. On the way back, I was carrying a 3000 pound car on the same trailer and averaged right at 12 mpg as indicated by the trip computer. I was running about 70-75mph(yes with trailer brakes and yes, lots of miles with a trailer) Also using a WD hitch.
So I 'm pretty happy with the towing ability of this thing. Gas milage is great, would still like a bigger tank, though. My last tow rig was a 99 Chevy Crew Cab dually with the 454, and it got 10 mpg unloaded and 8 witht he trailer, so you can see where my satisfaction comes from

On a side note, all of my computations from milage and gallons used have actually come in a little bit higher than what is indicated on the computer.