It's the AT4... 6.2L gas with 10 speed. Pulls like a dream. Trailer weighs only around 4,000 lbs plus the water tank was full, so maybe 4400 or so, but when we go off fully loaded with stuff it'll likely be around 5k. No Gray or Black water in it when I test drove my setup after they delivered it.
The trailer rating for the truck is 9,200 lbs. I have a load leveling hitch setup and set it so the truck is within about 1/4" or so from the unloaded level position. No squatting. IIRC when I first connected up it only squatted about 1 1/2" at the rear bumper which surprised me. After I set the torsion bars to raise it it came right into it and leveled off nicely.
I had a '06 Silverado(5.3L, 4 Spd auto) for 15 years and towed my 23' Continental enclosed car trailer(cars were about 3,500 lbs, total about 7,000 lbs) and it always struggled and I always had to drive in D3. The '06 was rated about 7,500 so I was using all of it.
Night and day between the 2. That's why I upgraded to the 6.2L, knowing I'd be better off, but didn't want to go the HD 2500 route or get into a diesel.
Rich
PS the last 3 photos..... I had 23 bags of bark mulch loaded in the bed when I took those photos. I was amazed how it held up. When I drove back from HD all loaded up it felt great. Amazing truck.