I think I would put some weight in it and see if it handles any better. 32' long, 13'4" tall, and only 14,000 lbs. Sounds like a pretty big sail to me. Oncoming traffic and when you are passing, wind load will be on the forward corners, and possibly deflected by the truck. When you are being passed you are getting hit on the rear corners of the trailer. It might just not have enough weight to keep it on the ground. I'll bet it handles bad in a strong side wind too.
-lee