Every time that I think I have a handle on these, they seem to explode in my mind. I know what each of the letters stand for, Gross Combined Weight Rating,........etc., and I know what they mean. What...
Your trailer weight is 18,500, which is over the Ford towing guide specs. You're also over on the GCWR. Not a big deal as it is most likely due to your 3.55 rear end. Just means the transmission may work harder. I'd give extra attention to your transmission maintenance, and watch the temps.
If you're happy with the way it tows then I would not worry about it.