Tongue Weight (getting sucked in by trucks)

Maybe I missed it, but the very first thing I would do is make sure tires are properly inflated (which for towing is typically MORE than for daily driving). Inflate the trailer and tow vehicle tires to their max pressure. See if it makes a difference. Trailer tires are intended to be at their max, and it doesn't hurt tow vehicle tires either, aside from possible wear issues if left at max inflation all the time.