I don't know how I stumbled onto this info but I found a web site that links to all of the manufacturer's vehicle tow guides. These are the raw specs for each vehicle including trim package, engine and gears.
Chevy/Gm are only for the last couple model years, Fords cover 99-10, Dodge 08-11, Nissan 05-10 & Toyota last couple of years
Hope this helps!
Truck Ratings for RV Towing