[Canuck]

I agree that a Diesel is the way to go for ultimate towing. When I bought My Yukon XL2500 in 03, there were no diesel options for the Suburban style Chev/GMC. I considered a Ford Excursion,because they offered a diesel. I chose the Yukon because it offered 4 wheel steering and beacause 90% of my driving is non towing and having tp park in conventional spots. My wife did not want to wrestle a 3/4 ton P/U around as well.
I just returned from a 6000 mile trip towing a 24 ft Well Cargo. After over 60 hous behind the wheel there was probably only 2 hours cumulative driving where I wished I had the grunt of a diesel. These were generally crossing mountain passes. For those instances I was down to 45-50 MPH and keeping the revs at 3000 -3300.
On the flat and modest grades the truck with 6.0 gas engine and the 480LE trans cruises nicely without a hint of 8000 Lbs out behind. I got 11 MPG on average for the trip.
If I had towing requirements more that 1 week a year I would switch to a diesel, for now the 4 wheel steering is the option that makes me want to keep the 03 for a while.