For what it's worth, I have a Trailer Life tow rating book, but it only goes back to 1997. In 97 through 99 models, a C2500 with a 6.5L TD and 4.10 gears had a trailer tow rating of 8500 lbs. It doesn't list a rating for a truck with a 3.73 axle.
Casey
1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter