2008 is 4-spd trans. Axle ratio is important as 3.08 performance and ratings is significantly different than 3.73 and 4.10. If you do not know, look in the glove blox for the RPO sticker. You will have one of these in your list:
GU4 : AXLE REAR, 3.08 RATIO
GU5 : AXLE REAR, 3.23 RATIO
GU6 : AXLE REAR, 3.42 RATIO
GT4 : AXLE REAR, 3.73 RATIO
GT5 : AXLE REAR, 4.10 RATIO
You should also verify you have Z82 in your list for the HD trailering package. That includes transmission cooler which is essential for any high walled trailer.
Assuming you have 3.42+, towing any high walled RV means 3rd gear, 2400-27000rpm on flat ground at 65mph. That's a lot like my prior truck. Downshifts to 2nd on hills at 4000-5000rpm. As Terryallan said, the truck will do that all day long (keep an eye on trans temp). The driver may not be pleased with that level of performance.
Stick to under 6000 pounds dry for a TT. That's 7000-7500 pounds loaded.
If you have 3.08 gear, just get a replacement truck. :)
