R -Vision Trail Lite Class C (B Plus) hitch upgrade question

We are looking at a Chevy based 2006 R-Vision Trail-Lite with a 6.0 Chevy engine on Chevy Express Van chassis. This unmodified chassis starts its tow capacity at 6500 and goes up to 9300lbs depending on the model. I understand that this is no longer the factory chassis and I understand there was a tow rating provided by the manufacturer for a reason….