Thanks for all the quick replies.  I'm running LT 285/55 20's, so I don't think the tires are the problem.  I did quite a bit of homework on towing capabilities and agree that airbags do not increase towing capacity (or tongue weight capacity), but they do help a lot with stability.  And, yes, pulling a 7,400 lb (dry weight) rig with a 1/2 ton is cutting it close.  Regardless, according all of the data I could get my hands on, I'm within the Tundra's capabilities, so long as I don't carry a lot of weight in the truck itself.  If I understand things correctly, cargo capacity subtracts from towing capacity by the square of the cargo's mass.  I had Camping World install the hitch, so I may ask them to adjust it and see if I can get better performance.
I was told this was an awesome forum, and for my first post, you guys proved them right.  Thank you again.  Looking forward to learning more.