i would not think it rear track but thats e z to check i would say something like a controw arm is bent or one of the arms on the spindles is bent as it travels it could pull thru and work close to bump steer ??? check for loose parts .bushings . i know you said he said it ok .BUT i work on many cars and trucks that we pulled the frame s on were the front end shop said were ok only to fined out that some front end parts were bent after they were done