I am casually truck shopping (waiting for 2014 models) and trying to fit a tow vehicle to a future 5th wheel. Most of the 5er models we like are in the 9000lb-11000lb dry weight and 12000lb-14000lb G...
If you stay within the payload & gcwr ratings of the vehicle it will be fine. If you think you need DRW then you should almost certainly be considering a diesel powerplant. A gas engine won't have the torque to comfortably tow more than #13k.