Need help with 454 missing

So far I've changed:
MAP sensor
Distributor, Rotor, Module, CAP
Spark Plugs and new plug wires
EGR valve
Oxygen sensor
Fuel filter
Ignition Coil
PCV valve
TPS sensor
Removed the CAtilitic convertor in case it was stopped up but it's OK

and the 454 still hsd a miss and hessitation.

ALL REPLIES are needed ASAP

I have an '89 2500 454 and when I originally purchased the car...I also was experiencing missing and hesitation. I took it to my mechanic and they solved this issue by correcting the timing. My timing was off...hopes this helps