It just seem like the first night i put them in it was very responsive, like i would go down the road and hit the gas and just right away it will pull and keep pulling. Now it feels less responsive and it does pull but in the higher rpm it just levels off and stops pulling. Im gonna go get my exhaust checked out cause there may also be a leak and that may be the problem im having. It sounds like maybe the donut gasket between the rear manifold and exhaust pipe is leaking. Hopefully that helps.