I haven't seen any else suggest this unless I missed it, but how tight are your friction sway bars? You might want to try tightening them up a bit I know when I first started towing I had what sounds like pretty much the same problem although my second sway bar pretty well cured it once I got the friction adjusted right, anyway I started trying them tighter until I got too tight you can tell because the trailer won't want to immediately straighten out after a turn. Then I just slowly loosened them up a bit until the trailer tracked right around corners afterwards the final thing was playing with the tire pressure. I finally settled on 45lbs. and now I can't feel most semi's pass unless they're the old broad noses ones traveling considerably faster than I am. And even then the push pull feeling is still not severe. Good luck I know this is maddening and dangerous but maybe one of us will hit on the right formula to help you.
