Have you checked for vacuum leaks yet? I had misfire over a cracked spark plug. Compression test and leak down test also just to check if you engine is healthy and valves are seating properly. Could possibly be a cracked exhaust manifold, leaking TB, intake manifold gasket. Make sure if you have hard pipes the hot side is not crushed. I quit using aluminum hot side pipe cause they bend way to easy with crap on the road. You should get a fuel pump rewire from Kinetic Kreations. That and the headlight rewire with relays are my first mod on any SRT4 I buy.