The OP says he has a '05 chevy 1500 HD which is the old 2500 truck.
The 1500 HD comes with a 8600 GVWR and 6084 lb RAWR with 16" load E tires. It has the 6.0 engine with the 4L80 tranny. Tow ratings go up into the 10200 lbs and a 16000 GCWR. Payloads up to 3129 lbs.
This info I have is a paste and copy from a GM website from that era which is no longer available.
Life... you can verify your truck is a 1500 HD by looking at the drivers side door post. It wiil show a 8600 GVWR for the 1500 HD or 6800-7000 GVWR for a std 1500 or the crew cab 1500.
If you have the 1500 HD then you have a much sought after 1500 truck.