Along with towing package that aesj2 eluded to, I believe the weight of the trailer and the truck are combined to determine whether or not they exceed the GVWR of the truck. (Also, the rear GAWR should not be exceeded.) A standard K20 has a GVWR of 6,600 lbs (RR GAWR of 3,880 lbs). A K20 with a RPO of C6P has a greater GVWR at 8,600 lbs (RR GAWR of 6,000 lbs). (The certification label on the door/glove box door should have the GVWR of your truck.) Unfortunately, your total weight exceeds these ratings. But, we know how 'we' sometimes push these trucks.