yep, it shouldn't be any surprise since the ratings are printed on the label right on the hitch itself....and you can't just 'bolt' on another that you would rather use. As stated, it's the rating of the CHASSIS that determines the weights that you can tow, not the hitch.
admittedly, downforce weight is not part of the chassis's ratings calculations, but it is for the hitch - the manufacturer certainly put 500# for a reason.
maybe you can find a 8,000lb rated hitch with a 800# tongue rating to 'switch'... but even the 8,000lb rating on a new hitch doesn't mean that your Chassis can handle up to that weight... you have to weigh your coach, fully loaded, and subtract that from the GVWCR for the 'towable' weight. I suspect you won't even be able to two 5,000lbs. Most coaches come with a hitch that's rated for much higher weights than the coach Chassis can actually handle.
sorry... : /
'14 Palazzo 33.3 bunkhouse 34' diesel
KingTailgater2 Dish HD, 100w/5a SOLAR, BlueOx
100,000+mi since '14 - US, Alaska, Canada.... formerly Georgia, then NorthCarolina, now Alabama : )