Mine vibrates pretty bad too. I checked the mounts and they all seem fine. A mechanic told me that sometimes if the exhaust is loose and moves around a little bit, it could feel like your whole car is shaking. I found out that the header on my car isn't bolted to the bottom of the car, so basically its just hanging there. When you hit the gas, more air flows through causing it to move around. So maybe check your exhaust hangers. Also check the axles