Car breaking up under boost now won't start

[Defcon62]

Hey thanks in advance for help, gotta be at work 7pm today.
Car is a 89 GTS 2.5 523
Passed somebody and car was breaking up over 10 psi and shuddering badly, ran fine afterwards for 15 or so miles. On the way home boosted again to try and get a idea of the problem, Car again broke up and then died. Pulled over and it would kick over and occasionally start and die. It would idle normal sometimes and rough like a couple cylinders weren't firing and then if I gave it any gas it died. A/F gauge was in the green while under boost.

I would tend to think fuel pump but underhood gauge says 55psi while cranking. Haven't yet tested for spark since I just got home from towing it in. Only codes thrown are 12 and 45 so thats no help. Fuel filter has only 1200 miles on so since replacement.

[Sittn86]

Check for spark & go here: Fault Code 45 It may be more help than you think.
Clear the codes first, then check again.

[Defcon62]

Just checked the spark, it seemed kinda weak, Car actually started up and sounded normal. Took it down the road fine until the boost needle got to 1psi and it died right there. Wouldn't start back up for awhile. Was limping it back to my driveway cranking in gear and it started. Seems to like starting that way for some reason. So right now any boost is shutting the car down immediately. While I had the plug out I checked the #4 piston and it looks ok, Car actually started with the plug out and i could hear good compression coming outta the cylinder.

[Sittn86]

You can't check compression by listening to air. Where is your boost gauge connected? There might be a leak before it, causing you to only see 1 PSI. Go through the diagnostics for code 45 at the link I posted.

[Defcon62]

Unsure of the boost gauge connection as it was installed by the previous owner, I'll dig through the vacuum lines, its likely though that its connected to the vacuum block. I'm gonna run through the checklist like ya said. Its kinda blowing my mind that any boost causes the car to die. What else should I check aside from the link you provided?

[Sittn86]

Do that first. Your solution is probably at that page.

[Defcon62]

OK vacuum lines check ok and car is holding 20 inches at idle which is normal. Revved it up while sitting and it sounded ok the first couple times then bogs and dies. Won't start unless it sits awhile.