93 Eldorado problem need help

PROBLEM WITH INTERMITTENT "MISSING"
Sorry this is so long, I wanted to give as many details as possible. 4.9L NON-Northstar, in a 93 Eldorado
Missing in Cyl 3 and also 4. INTERMITTANT. Driving down the highway at 70mph+ it runs like a top -about 90% of the time. Sometimes in city driving, runs great (10% of the time). Sometimes feels like just ONE cylinder missing, other times, like both are missing. Sometimes I can start it and it will run like a top for 5, 10, even 30 minutes (I call this a "Good start"). Other times I start it and it it's running rough from the get-go (I call this a "bad start"). If it is running good, 2 minutes later it could be missing. if it's missing, 2 minutes later it could be running great. But it does seem to run good almost all the time when cruising 70mph and up, and tends to run bad almost all the time when cruising around 25mph.
When it's missing, the RPM needle jumps up and down spastically. The needle gets crazier the worse the engine is running.
I was able to access the computer thru the climate controls, and there's no codes that could possibly be related to engine missing (had a TPS error, replaced TPS and that error is gone). In that computer access, I was able to disable injectors, when I disabled Cyl 3, there was no difference in the idle (indicating Cyl 3 was currently not firing). One time when it was REALLY running bad, neither Cyl 3 or Cyl 4 were firing.
WHAT HAS BEEN REPLACED:
- All 8 Injectors with rebuilt from Linder Technical Services (highly recommended by CadillacForums.com, voltage/flow tested, flow matched to +/-8%, and guaranteed)
- All plug Wires
- All Spark Plugs
- Distributor and cap (not the coil)
- Battery and battery connections (also inspected all grounds, all were totally clean)
- TPS
- Alternator was tested by a reputable shop and tested out fine
I'm about 95% sure this is electrical. since it seems to me that if mechanical, it would miss 100% of the time (ie. Valves or bad cylinder, etc.)
Tonight I think I confirmed it being electrical.. I was driving with windows down, car was in it's "bad running" missing on at least 1 cylinder. I then put up both windows at the same time, and the instant that they were fully up (and I was still pushing the switches up)... the car STALLED, engine to "0" RPMs!
WHOA... did that really happen? I let off the switches and RPMs back to normal! Then I again just tapped BOTH window controls up, RPMs to "0", I let off, engine running again. I could repeat it.
Then I had a stop, turned it off, started it back up, now the car is on one of the "good" starts (ie. no missing!) so I tried the windows again... car KEPT RUNNING, the only thing was the lights dimmed pretty badly. But the RPMs didn't go to "0".
A while down the road, car started missing again, so I tried the windows and BAM, RPM's to "0".
For what it's worth, I pulled up Battery Voltage and it never wavered or changed even when I did the window switches.
So it seems when it's acting up, the window switches kill the engine. If it's running good, they only dim the lights.
Any ideas on where to start looking for this problem? People on CadillacForums are suggesting I replace the Coil next. I have no problem doing that but I don't want to keep throwing money at non-problems. If I have to spend the money on a new computer and that fixes it, then I'll spend the money!
HELP PLEASE!!
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Tim you need to take a "PCM snapshot" of the engine data while the engine is running and missing. Your car has On-Board diagnostics capable of taking a snapshot, this information will help diagnosing the engine miss, by letting you see what the engine is doing when it is missing. I can send you the procedure if you would like.
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Was told by another owner with same problems to change the chip in the computer. He had the same issues and that solved it for him. I have found one for $80 and will give that a try.

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NOT going to pay for a question answered. I have found many good people willing to help one another for NO charge.

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I have a 1990 Cad Eldorado. It is acting like it wants to vapor lock. It is inconsistant with this problem. If it sits in the heat, and I start it, it sputters and dies and acts like there is a fuel problem. I have replaced the fuel filter, fuel pump and computer. It still has the problem. It has been in the shop for over a week. I am really at a loss as is the mechanic. Jana
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