I would check with the GM parts counter and get an updated fan clutch. This has happened to me on my 2004 and it ended up being a TSB and they replaced the fan clutch. No more problems.
Had Hankooks for 20k miles and they were very nice right up until they got noisy. Replaced them with Michelin LTX M/S2 and couldn't be happier. I was also surprised how well they worked in the snow.
I was in the market for a hitch as well, after someone rear ended my truck with the open trailer attached. Looked and narrowed it down to a Curt 15108 or 15521. I tried to find the differences and except for weight rating, I went with the 15108. 12K should be plenty. The 15521 took up some space...
I just replaced my Hankooks with some Michelin LTX M/S2 tires and I'm pretty happy. The Hankooks are a good tire, but after 22K, they got fairly loud. I would say that you can get at least 30k on the Hankooks with care. The Michelins are nice and quiet and the truck almost seems to "glide" now...
V-leds are definitely pretty bright, but I've been through 1 set of license plate lights and 1 rear stop lamp already. I would think they would last a bit longer.
I had a similar setup to yours and I coded out at about 35k. Turned out to be the EGR motor being gummed up. I took the plate and stick out and drove it hard a few times and it cleared. I have switch to EFI since then, and haven't had any issues since then.
I would have the dealer fix the code before putting the stick in. IIRC, the stick will prevent certain codes and not others. Also please solder all the connections. Saves headaches in the future.
I get it when I plow snow sometimes. It's the boom boom boom from the rear axle when it sometimes tries to search for traction. I clamped down the springs and have not had it since. The rear feels more planted to me now.