Your truck's GVWR - gross vehicle weight rating and the maximum it can weigh - is 9200 based on my research ( http://www.pirate4x4.com/tech/billavista/Chevy/specs/ ). That means your maximum pin weight is going to be 9200 minus 7880, or 1,320. The GVWR is the thing that you always run up against with a 250/2500 series truck and a big fifth wheel, the 3/4 ton trucks just do not have the payload for a heavy trailer. If you tow that trailer you'll be around double the allowable pin weight rating for your truck. GVWR is the number that matters, the tire ratings don't count (but should not be exceeded, which you won't if you keep to your GVWR).