running rough

Hey guys,
I've been trying to think of what the issue could be with my Cutlass. I installed a new cap and rotor and a week later the car started running bad. The car runs ok from idle-1900rpm but runs terrible from 2000rpm on up. It has occasionally backfired.
List of new parts,

• Spark Plugs
• Spark Plug Wires
• Fuel Filter
• Fuel Pump
• BWD ICM
• BWD Ignition Coil
• MSD HEI Cap and Rotor

I've made sure that my firing order is still correct and it is. I'm wondering what else could be the issue.

@DoubleV
Backfiring out carb. I haven't check'd timing because it was fine last I knew. I have check'd the cap and rotor many times for defects but can't find any. Cutlass doesn't have a catalytic converter. As for when it started acting up, it ran fine one day and not ok the next morning.

@olds307
Spark plugs are ACDelco, Wires are MSD, Fuel filter is Mr. Gasket (made of glass with the replaceable filter), and I don't remember the brand of fuel pump but I can see it pumping fuel.

@pontiacgp
I am using wire spacers so they aren't cross arcing.

@pontiacgp
Plugs are 4 moths old. I'll look for a cracked one just to be sure.

@Pontiac455
I just don't get the feeling I have a fuel problem anymore.