My 04 LS had a broken spring in the left shock (loud, dull rattle), so I took it to my Tires Plus because I needed to rotate and balance the tires. They replaced the front shocks and did an alignment. I've literally had to take the car back three more times because at higher speeds, it pulls to the right. You can tell the alignment has been properly done because the steering wheel is lined up straight. But on the highway especially, when I let go of the steering wheel, it bumps right. What could be causing this? They tell me there's no caster adjustment on this car. What could make the car do this after replacing shocks?