2002 Mitsubishi Eclipse Problem with 2002 Eclipse GT

I recently changed my valve cover gasket and when I start up the car, the engine is shaking/vibrating in a not normal mode.I checked all the connections to see if there is anything left out and they were all connected. My exhaust smells weird, and it's like it's choking or something. Car is idling very weird especially if I put it into gear. The exhaust is what's really crazy. It;s making this choking sounds like those car that the exhaust fires or something when shifts gear.
Any suggestion would be really helpful.
Thanks alot in advance!
Donald