Engine Performance problem
1999 Plymouth Breeze 4 cyl Front Wheel Drive Automatic 130000 miles

i have a 1999 plymouth breeze expresso the motor is the 4 cylinder 2.4 litre it took a while to get to 90mph so i was messing around and bought a speed chip and it woke it up plus gave me much better gas mileage and i did research on the car and it looks awsome with ground effects the car was sent for a new timming belt and they messed up the timming 3 times.. the car has ever since ran rough at idle since the belt repair some times when easing on the gas the car goes then has a dead spot kinda like a spudder..and i ended up buying a nice tail pipe for it and it sounded amazing but now i noticed when it shift at hard acceleration it doesnt shift with strong shifts it almost spudders when it shifts when it shifts it seems like a spudder but isnt almost like it jus dogs the motor down for that second its weired also at rough idle the car rumbles...do you think maybe they bent my valves by messing up the timming? or could it be a dirty fluel injector or something i cant figyer it out im a muscle car guy haha oh and the car still runs strong and has power it odd....thank you for your help