Here is my understanding of the rating situation on the new motor homes. Like you I have a 5000 lb hitch which can be upgraded to a a heavier hitch which would usually be 10,000 lbs.
So my manufacturer told me that sure you can upgrade and tow up to the GCVWR. They just won't warranty the Coach. Why? Their theory I'd that with the 10000 lb hitch, I might be stupid enough to load it to 10000lbs which would be over the rated 22,000lbs to 24500 lbs.
Crazy logic if you ask me, however they have told me the provided hitch is very robust.