I don't personally know anyone that owns one, but I see a few now and then.
There was alot of discussion about the oil pump belt having to be replaced at some point. Latest info about that (newest engine design) is replace it at 200,000 miles or at 15 years, whichever comes first. I also read...
Towing test, if you are into watching the TFL Ike Gauntlet test.
https://tfltruck.com/2023/04/video-new-2023-gmc-sierra-1500-duramax-lz0-diesel-vs-the-ike-gauntlet-the-worlds-toughest-towing-test/
Also found this info, don't know how accurate it is. Possibly the heated seat fuse is the same one for the ignition?
https://www.startmycar.com/us/chevrolet/silverado/info/fusebox/2006#anchorfusebox1
Other people having issues also.
https://chevroletforum.com/forum/silverado-sierra-fullsize-pick-ups-21/2006-silverado-heated-seats-works-itself-26370/
Wished I could help you, but my 2006, Chevy 2500HD is not a luxury model, :D therefore I don't have the heated seats. I would be looking for a fuse to pull or try what smokymtn65 recommended.
Sounds like you are making progress. You mentioned the camper being like a wind sail, yelp I agree. My 21 foot camper probably weighs 4000 pounds or so. With my Duramax, flat lands, I might get close to 13 mpg if I drive decent. In the hills and mountains, It's in the 12's, I did see 11.5...
Speaking of Dorman body mounts, I recently ordered 2 from Rock Auto for my S-10 daily beater. Great replacement product and easy installation. Wasn't replacing all 6 of them, just the ones that went bad for now. Just my beater, local truck, no big trips in it. I just fix what breaks and move on.
I'm curious about the tow vehicle? If it was single wheels on the rear axle, I bet it's tire ratings were greatly exceeded. Also, probably the axle rating was exceeded.