It is most definately not the trac control. I turned it off and it still does it. Any other suggestions?

 

with some "traction bars" aka "long bars"

 

I'd try dropping the brushhog, scale all the axles and hopefully you'll be within the weights. Then if you can recreate the problem, take it to the dealer with the loaded trailer. Not that you can't tow that configuration, just get everything within the posted ratings and then make the dealer explain/fix it.

 

^^Probably a good call...