A 20' 8" beam equipment trailer with 2 x 7,000 lbs braked axles weighs approximately 3,600 lbs, add your 5,000 lbs of MX5800 and fuel / loaded tires you are soon above 9,000 lbs in total weight. Not sure of your year or model of GMC 1500 pick up but you may be overloading, a new GMC 1500 has a...