New tow tug

I just bought a new travel trailer which weights about 6000# and has proven that my Ford Expedition is a wimp. I want a long wheel base GM SUV 04-06 with a 6.0 litre motor. If I understand correctly that leaves my choice down to a 2500 Yukon XL or a Denali 1500 XL. I'm looking at both right now in low mileage lease backs and the Yukon has quad-steer. Do I need to go to the 2500 which is presumably a little heavier on fuel or would a 1500 with 6.0 litre do the job?
Thanks for any advise