Wow, I'm actually doing this. Okay! Here we go.

Backstory:
About 2 months ago I was low on gas driving threw town and the 200V70 XC stared cutting in and out. I didn't think much of it because the gauge was a little low. Pulled in got gas went on. It didn't cut out for the rest of the day. Next day it cut out or surged quite a bit. (Put in fuel cleaner thinking it was bad gas)
The problem progressed into me having to wait until it reached running temp before it would run on all cylinders. It would "click" then I would rev it up and it be fine. Driving it home one night it started cutting out BAD! I had to downshift to keep rpms up(auto transmission). Got home and the Cat was glowing red.
Thinking it was a bad catalytic converter I chopped off the original and put another one one. That didn't fix anything. It had melted the inside of the cat. It had thrown or spit out platinum out of the tailpipe by me driving it in "limp home" mode.
For a while I tried to do what I could with troubleshooting until one day I couldn't take it any more. I took it to the shop. Those lying bastards here (in Hawaii) do to know a Volvo from a dick in their own ass. Told me the ECM was fried and it would cost $2grand. Took them a computer and they said they plugged it in. But it needed to be flashed.

Yesterday I started with the basics on the car. Okay it was missing. I troubleshooted the fuel injectors. They all work. I switched the coils around, I have one dead but the car is still only running on the 1 and 2 cylinders. Today it did something it's been doing every once in a while. I had left the key on and I disconnected the battery. After I switched everything around I connected the battery, went in to start it and the dash "black" lights were all on. I turned the key off, back on then started it. It ran like it only had one bad coil. There was a miss but not a "limp home" missing on three cylinders missing. It started fine, then "tick" it declined on rpms and ran like again.
Is it the ECM?
What systems are checked after startup?
I'm at a complete loss and I have 5 grand into it, I can't afford a 4 grand loss on this car because it's not running right. Please throw some real info my way.