Hi Jim, congrats on your setup.
I have the same truck/trailer combination that you do, and with the advice you've been given you' ll find that towing is a breeze. I've got a basic WDH with 800lb bars and without sway control, and haven't had any issues with how it tows.
Only issue I've run into in well over 10,000kms towing with this combination was when the tranny temp on my Sierra hit 100 celsius briefly on the Icefields Parkway in the Rockies.
As far as payload capacity goes, I usually have the bed quite full with 4 bikes, a full cooler and a large Rubbemaid with supplies all strapped in there. That being said, with the fresh water tank on the 21rs under the front bunks, we dont travel with full tanks, as you'd want to keep an eye on the tongue weight.
We originally towed our Roo 21rs with a Jeep Grand Cherokee, and upgraded to a 2010 Sierra for better towing and what a difference! The first time I tried the engine braking, you couldn't wipe the smile off my face! It is so much better than getting pushed down the hill by the trailer like we had in our Jeep GC...
Happy camping, enjoy and let us know how it goes!
2009 Roo 21RS
2010 GMC Sierra 1500 w/ tow pkg
Nights camped in 2014:29 | 2013:33 | 2012:32 | 2011:33 | 2010:30