It sounds like you need more of the tractor's weight forward.
I haul a John Deere 750 with front loader and box scraper on an 18' trailer. I make sure that the tractor's weight is more up front than the rear. But I also tow it with an F350 Dually.
BTW..I went with a girl who worked for the tractor company in PA. but being I lived in CA it was a long distant affair. I guess she got lonely and found someone else then wrote me a John Deere letter.

Sorry, I couldn't pass that up. Good luck.