92′ Olds Cutlass Supreme S w/ 3.1 eng.

My 92′ Olds with a 3.1 v-6 starts and runs fine for a few seconds, then it hesitates, misses, gets worse then dies.

I replaced :

Fuel Filter, Fuel Pump, Removed and cleaned all carbon from EGR and replaced it, separated exhaust from catalytic converter,

and installed a new Crank Position Sensor. I fired it up and same thin still happens! Is it possible timing chain/belt? (does backfire at higher rpm before stalling). Could it be a Cam sensor? or can a faulty coil pack be the culprit? how can I test and eliminate these possibilities? or is there something I may have missed?