Well, here's my specs:
* 2007 Chevy 2500 HD, 6.6 Duramax Diesel, Allison Transmission, Roadmaster Active Suspension on the rear and Bullydog Tuner
* Sabre 32 RCTS 5th Wheel
Had my rig weight at a local truck Cat scale:
Truck Alone: 7,120 lbs (3,980 front axle / 3,140 rear axle
Truck & Trailer: 18,240 (3,960 front axle / 5,540 rear axle / 8,740 trailer axle
According to the Owner's Manual:
Maximum Trailer Weight: 15,700
"Fifth-wheel or gooseneck kingpin tongue weight should be 15% to 25% of trailer weight up to 3,000 lbs maximum"
"Trailer rating limited to 12,000 lbs with weight distributing hitch."
Checked the specs on the OP 8.1 gasser...depending on the rear axle, he should be able to get the same or a bit less than the specs for my vehicle above.
Love the Duramax! Mine pulls great and I get about 10ish mpg going 65-70. (Better than I used to get with my 1500 van with a 5.7 pulling my 1972 6,000 lb Airstream)