Help - I don't want to kill my truck with my trailer...

I have a 1500 GMC Savanah AWD Van with the 5.3 and towing package pulling a keystone Cougar. Tow rating on van is 6200. The weight of the trailer is 5900 lbs including water and propane with empty waste tanks. When we ordered the trailer, the weight was supposed to be 5400 but they changed the model and made it 18" longer and 500 lbs heavier which they didn't notify us of. Anyways,we just completed a trip from Pa to Yellowstone going through 10 states.We had no issues at all with the tow vehicle.