Getting truck and camper weights with and without the camper connected is the first step. You may have removed weight from the front axles with improper WDH adjustments. Unloading the front causes an unstable feel in the steering wheel. Verify your truck front axle weighs close to the same with and without the trailer connected.
Air up your truck tires to max pressure as stated on the tire sidewall will help. Timbrens will help. Unfortunately, I don't think you can ever totally eliminate the push/pull feel you get when passing large trucks or the effect of crosswind.