When does it wander? Is it a constant, is there a speed that it's more noticeable, is it in one direction more than the other and when? Do certain road surfaces change it, etc... how are your tires wearing? I'm just posing some questions that I would ask myself in trying to identify the cause. I would also be looking at the rear tires for wear and all of the fasteners, bushings, etc, and making sure that the rear end is not moving and is retaining alignment relative to the frame. Are the rear springs allowing more deflection than the front or allowing it to sit at an angle when loaded? Weight transfer can cause wandering. How much does the rear move? you mentioned that you aren't running rear shocks. When you initially aligned it, was it loaded to simulate a driver? Just a thought. Also, I would look at the brakes... I had a brand new truck that was in and out of the shop for alignment issues, they changed the gear box, re aligned it, different tires, etc... finally, at about 40k miles the rear brakes started squeaking. I tore it apart and one side had the stainless steel anti rattle clip damaged just enough to allow one corner of the pad to hang up. That was the cure. I had personally walked around the truck with a infra red thermometer and checked rotor temps, jacked it up and spun the wheels, etc and could not detect the problem. It seemed to get worse as I got up to speed, it would climb the crown of the road and change lanes to the left if I took my hand off of the steering wheel. Moral of the story, don't overlook anything. I've also had debris get inside of brake hoses and act as a check valve on occasion and drive me insane chasing intermittent problems. If everything checks out, you might try switching the wheels from side to side just to see what, if any effect it has before spending money on new tires. Hope you find the issue soon!
