Per E trailer:
The big differences between a Class IV and a Class V hitch are the capacities and the opening size. Class IV is going to be a 2 inch hitch opening that has tongue weights typically up to 1,200 lbs and total trailer weight of 12,000 lbs. For a Class V hitch the capacities bump up to 20,000 lbs for the total trailer weight and 2,000 lbs tongue weight. Typically this hitch will have a 2-1/2 inch hitch opening but there are some 2 inch sizes available.
Maybe you need to upgrade to a class 5 hitch?