I just had a new exhaust put in my car on friday, my old cats were dead so he did new high flow cats and a magnaflow muffler. I couldn't pick it up then; so, he locked my keys in it and I picked it up today.Well, the car shakes like no other now. When I am sitting at a light it feels like I am in a 1966 mustang. It is the same when I accelerate it sounds and feels terrible. I had to go one exit on the freeway and didn't want to go over 60 because it felt like the thing was going to die or something. Any ideas or thoughts would be great. I am just not going to drive it for the weekend and take it back to him monday to figure out what the deal is.

 

ITs probably not welded on good. They probably just need to put some more brackets on it.

 

Take it back. Make sure that they reconnected the oxygen sensors, and that everything has enogh clearance.

Did you have the resonator removed too?