I have a Chrysler Sebring 2000 and it will turn on but then all of sudden stop working it makes a jerking noise b4 turning off and its not the transmission because that has been changed along with the motor any idea? I think it might be the fuel pump but how do i know for sure?

Fuel pump is a posibility, but they usualy fail completely rather than work intermidintly. If the engine or trans was changed very recently Maybe a sensor unhooked or un adjusted. Have to scan it with an obdII scanner to check your codes but some of these chryslers had the crankshaft positioning sensor on a kind of slotted adjustable setup running off the torque converter through the transmission bellhousing.
I have put them together before and the car ran with a heavy tic when first started then chugged and died. The scanner told me loss of crank or cam sensor so i new what I messed up right away. Lossened the bolt and backed the sensor off and it ran fine. Of course I dont even know which motor you have, or if it has the adjustable sensor. First thing you need to do is have it scanned.