I have a 2001 Toyota Tacoma and currently have a 5 point harness car seat installed. The problem is even with a top tether, 2 side tethers and a seat belt across the back of the car seat, it shifts more than 1" from side to side. Myself and others have tried to tighten the straps to get the car seat more stable but to no avail. I'm consider moving my 3 year old, 32 lbs, 38" son into this Graco booster seat thinking it might be more secure. I need to some feedback as to what I should do. thanks!