Longbed tailgate will hit camper when hitching

It is the design of the fiver that causes this. Not a truck issue. My Cougar is the same way. It got annoying, and I thought even a little dangerous, to have to get out and close the tailgate in the middle of hitching and unhitching. I solved the issue by going with a Vee gate.

The axle should be the same distance from the rear in a short bed and long bed truck in the Ford. The extra length is forward of the wheel well. But can't say how your hitch was installed in the old truck.