reo4ua,
The Yukon XL does sound like it would be a pretty good tow vehicle. Especially with the 4.10 gears. The only thing I worry about though is not the engine, not the rear end, but the suspension and its capability to handle that large of a trailer.
I have a 2011 28BRS and I used to two it with a 2000 GMC Ext Cab 1500 with the 3.73 rear end, tow package, 5.3L engine, etc. I also had the weight distribution hitch and all the correct towing equipment, but it just never towed my trailer like I wanted it. I had a lot of sag in the rear end and I was always quite particular about how I loaded the TV and TT. I would always equal out the weight the best I could. My truck sagged down quite a bit in the back and would never stay in overdrive while I was towing. I would be pulling it at 60-65 mph down the interstate and I would be at about 2800rpm. I could literally watch the fuel gauge going down as I drove every mile.
Plus, I just never felt comfortable in the drivers seat. The trailer always felt very unstable behind me. Especially with any sort of good cross wind. I played with the settings on the hitch quite a bit and it still didn't tow as well as I wanted it to.
I recently bought a 2007 Silverado 2500HD crew cab with the 6.0L motor. I haven't pulled my trailer yet, but I did pull a buddies from the dealer to his storage facility after he had some work done. His trailer is slightly over 30ft and probably weighed about 2500lbs more than mine does loaded. But my truck handled it wonderfully. I was even getting about 13-14 mpg's going down the interstate. The 6 speed transmission that I now have did wonders compared to my old 4 speed. I was thoroughly impressed with how stable the entire rig was while pulling. I was much, much more comfortable pulling his trailer than I ever was pulling mine.
There is just something to be said about having a TV that is actually suited to pull large trailers like we have. The difference is amazing between at 1500 and a 2500. The decision is purely up to you, but coming from someone that used to pull with a 1/2 ton, I would honestly never go back. Just the stability in the vehicle alone is worth the extra money!
Thanks for all the replies. In response to your questions, 5.3l v8, factory tow package, 4.10 gears and 160k on odometer.