Here's my set up.
2006 Chevy 2500HD 8.1 - 3.73
2011 XLITE 28BH
According to the manual GCWR of truck is 20,000 LBS
GVWR of TT is 7580lbs
Curb weight of 2006 Chevy is 5750 lbs
According to the owners manual I can haul in OD if I'm under 75% of GCWR of 20,000 lbs. Thus I can tow in OD if I'm under 15,000lbs GCWR according to the owners manual.
If my calculations are correct I have 1670 to play with after taking into account the GVWR of the TT and and the curb weight of the TV. I realize curb weight does not include passenger weight. So if I take me, the wife, and 3 kids that's 560lbs. I still have about 1100lbs to play with in regards to loading up TT and TV to stay under the 15,000 lbs. Would I be pushing the limits with my tranny and tv if I tow in OD at cruising speeds?? It would drastically improve my gas milage if I can safely tow in OD. I mostly tow in very flat farm land terrain.
TV:2006 Chevy 2500HD 8.1 Vortec - Allison Tran
TT: 2014 Wildwood Heritage Glen 300BH