I recently bought a 2008 Surveyor SV-291 that I'm towing with my 2006 Yukon XL.
This truck is (from an power train perspective) a Chevy 1500. 5.3l V8 flex fuel with a 4l65e Transmission.
I added a 40k GVW transmission cooler and a ScanGauge II to monitor the transmission temps. Prior to the cooler I sat around 176F, after the transcooler the truck barely gets over 125F while pulling. It gets up to about 190 (highest I've seen it go) when the truck is idling for 10+ mins. This is a result of the fluid being warmed up as it passes through the radiator by the engine coolant.
The faster you go the lower the temps it seems, even when pulling up grades the temp does not climb hardly at all. I'm very happy with the unit, it replaced the factory tow package cooler, and will hopefully provide a longer life for my 4l65e.
I also put some lucas oil severe gear 85w140 in the rear diff, and replaced my track bar bushings and the truck tows beautifully when the Reese hitch and 1200lb bars. I'm really impressed. I was very afraid that I was going to end up wanting to buy a heavier duty truck because I would be "white knuckle" driving with a 1/2 ton