research on your TV, now we have factual information to work from. Crabman did an excellent job of sorting through all the numbers, so I hope I don't add any confusion to the discussion
Just a couple clarifications:
* GM RPO Code of "GU5" = 3.23 Gear Ratio
* GCWR of 11,000lbs: As Crabman stated that is the "maximum combined weight" that your TV and TT can weigh. The 80% rule doesn't
get applied to this number.
* Tow Rating: The "published" Tow Rating for your TV is 5,700lbs, but this rating is based on the "curb weight" of your TV. The combined weights of any TV options, TV passengers, and TV cargo must be subtracted from the "published" tow rating to get your "actual/real"
tow rating (http://www.jaycoowners.com/showthread.php?t=3866
* 80% Rule: This is a ballpark approach to sizing the maximum GVWR of a TT to a specific TV when only the published tow rating is known. By taking 20% from your 5,700lb tow rating leaves you with 4,560lbs, so by using this method you shouldn't purchase a TT with a GVWR that exceeds 4,560lbs.
Basically the 20% that was removed accounts for the combined weights (ball park) of the TV options, TV passengers, TV cargo.
* Payload of 1,913lbs: The combined weights of the TV options, TV passengers, TV cargo, and the loaded TT tongue weight can not exceed the payload weight.
* TT Tongue Weight: Please note that the loaded weight of any TT is subtracted from the payload/cargo capacity of any TV.
* The TT's loaded tongue weight is also part of the GVWR of the TV when in tow.
Limiting factors of your TV:
* 4.8L Engine/3.23 Gear Ratio (great for the highway, not ideal for towing)
* Limited Payload (as are most 1/2 tons)
* Actual Tow Rating (is what-it-is)
Since you already have the TV, confirm your TV's loaded weight to make sure that you aren't loosing some towing capacity with the 80% approach. Take your loaded TV (passengers, full fuel, cargo) to a CAT scale and weigh it....,the 2nd forum link I provided above references this process.
Another approach at the CAT scale is subtract your gross CAT scale weight from your TV's GCWR of 11,000lbs, the remaining is the maximum you can tow.
I based my response on your posted findings. Although a moot point, I did find the following data on your configured TV reflecting some different weights (if this is your TV): http://www.cars.com/gmc/sierra-1500/...=USB70GMT179F0
I hope this helps a little.