With a 2650S, I tow a car I race on an aluminum trailer. Total package can vary between 5,200-5,500lbs and never had a problem. My trips are normally 200-400 miles.
In mid-2014, the hitch was upgraded to 7,500lbs/500lbs. The only part of the hitch requiring strengthening was the chain loops. Reference:
http://www.forestriverforums.com/for...s-47823-2.html
Someone posted $310 for the upgraded hitch and installation. I may do it just to be legal.