Welcome to iRV2 .
I'll assume your current hitch is a Class IV , so if either Freightliner or Tiffin can supply you with the manufacturer and part number for your existing hitch , then contact the hitch manufacturer with the info and ask about a Class V.
Be warned that the reason there is only a Class IV on your coach is probably related to frame strength, chassis brake system and/or transmission GCWR.
So an increase in hitch strength doesn't mean you can safely tow to the hitch capacity.