The factory receiver hitch on my bro's '06 F350 has some strange specs.
You can only pull 15k# with a suitably rated 2.5" tube hitch. If you adapt down to a 2" tube, you can only go to 12.5k#.
For the life of me I cannot find any sort of 2.5" tube hitch that is rated more than 12.5k. I can...