Tim, there was a prior thread that may help your question. Goto
The year and the size of the hi-lo may have 2" or 2 5/16" ball size. The factory used both sizes. My 1997 21 ft Tow-lite has a 2" ball.
Your best bet is to take both sizes & a box wrench (the nut size & shaft diameter may be different, so check this)
There is also another tread on this message board that refers to the weight distribution hitch. Under chit-chat/tow vehicles/tow systems
I would recommend a wieght distribution hitch.
When you buy your wieght distribution hitch, buy one to accept a 2 5/16" ball size.They sale a reducing bushing to accept the smaller shaft size of a 2" ball.
I used the reducing bushing on my set up, since I had an older wieght distribution hitch with a 2 5/16" ball.
Also, you may need an electric brake controller for your truck.
LES 97 21ft. towlite