Luckily I downloaded and saved all these old order guide PDFs from way back then.
Attached is the GM order guide for 2006 Silverado 2500HD
Publication date is 7/28/2006
Towing specs start on page 63
With (LLY) or (LBZ) Duramax 6.6L Turbo Diesel V8 /Allison trans./3.73 axle ratio, the Gross Combination Weight Rating (GCWR) is 22,000 lbs.
I also added a few more related order guides just for the heck of it.
The 2007 Classic 3500SRW (9900 GVWR) has the same max. GCWR as the 2500HD: 22,000 lbs.
The 2007 Classic 3500DRW (11,400 GVWR) has a max. GCWR of 23,500 lbs.
The last two PDFs are the early order guides for the new body style 2007 trucks, and I didn't see any towing specs.
Last edited by GoneNomad; 11-24-2011 at 08:38 PM.