Runs good (smooth no miss) up to 4000 rpm, then flattens out and will not go beyond 4000 rpm and makes a popping sound (missing), and the service engine soon light starts to flash and if held there long enough will stay on until reset. Acts just like going to the rev limiter in park, except for the flashing service engine soon light.

Replaced the spark plugs and swapped the coil packs to see if fault would change, no help.

Not sure what to check next, could it be a defective ICM or PCM or maybe a clogged cat?
Any ideas or advice would be greatly appreciated.

Thanks Greg

Have you changed the plug wire? The flashing SES light is the misfire. Generally caused by a weak spark. Can also be a bad fuel injector.

you try swaping the #1 wire with something else? that would be next on my trouble shooting plan

I'll try swapping the plug wire and see if the fault follows. Just wondering if one cylinder misfires, would that keep the engine from exceeding 4000 rpm while driving?
Thanks Greg

A flashing check engine light while typically caused by a misfire is actually "a potential catalyst damaging condition". per the FSM.

Did the plug have any damage to it?
I'd aim next to ICM or CASE (crank variation learn) before swapping pcm

I would look at the fuel injector on that cylinder next. Is it firing? Is it getting a signal? Any signs of a fuel leak (bad O ring)?

You will have bigger problems to fix than a misfire if you continue driving your car at 4,000 RPM'* with a misfire. For example, if the misfire is related to a lack of spark you are dumping raw fuel into your exhaust, and your cat will go boom.

I was unable to swap #1 plug wire as it would not reach any other cylinders so I installed a new set of AC/DELCO wires. Cleared the codes and went for a test ride. Same results almost, still flattens out at 4000 with a miss (sounds like popcorn) if I hold it long enough, about 10 seconds the SES light will flash and set a code. Now the code is P0300 multiple or random cylinder misfire. Plugs and wires at 95000 miles is like regular maint. I guess my next stop is to have Mr.Goodwrench put his diagnostic computer on it before I start throwing electronic parts at it, unless someone has seen a simular problem. Any ideas?
Maybe check fuel pressure or change the fuel filter.
Thanks Greg

FYI : Changed fuel filter and did not fix problem, overall the car runs better but still misses at 4000rpm.

Fuel pressure wouldn't miss in a single cylinder. It would miss on all of them. Still worth testing though. A clogged injector could cause a miss. For the most part, a misfire is ignition. I believe you said you swapped coils and no change. Another thing to look at is the terminals on the ICM. A defective ICM can cause a misfire on 1 cylinder. If everything else checks out, then your down to mechanical problem. A bent or burned valve, bent push rod, bad rocker, broken valve spring.

Ok, so I saved 30 bucks using advance auto parts coupon code P20, but a new ICM did not fix the missing either. Bummer. On the bright side I now have a spare ICM for trouble shooting.

Greg