Pulled to the left when being passed by Big Rigs

I was taught this back about 1960. When a large vehicle is about to pass, maintain a steady speed while gently and manually applying the trailer brakes. This pulls your rig into a straight line and greatly reduces trailer sway.
This also works to reduce/eliminate trailer sway from other sources.

You may waste your money on air tabs if you wish; a large trucking company did wind tunnel testing and proved they are not worth the investment.