Rapid backfire/misfire

[90 DGRZ]

I'll try to keep it short.

blacktop, exhaust, FMIC, hks t28, 10-11 psi.

I had a cage welded in my car (battery disconnected) about close to a month ago. A month BEFORE that, i didn't really drive the car at all since it's last event. when i got my car back from being caged, i took it around the block the day before an event, and it rapid backfire/misfires around 4.5-5k and loses power and stumbles. (sounds like back to back rapid gunfire) as long as i hold it WOT, it will do that, and eventually slowly make it way up the tach. Sometimes, like in second gear, it really won't stumble or backfire, it will just climb up the rpm range powerfully, then around 5k the power will seem to "flatten" out and will eventually pull to redline. but most of the time, it's the back fire issue. This only happens under load, the car revs fine in neutral.

The reason why i mention the car being caged, is because i really don't know if it's coincidental that it happened after being welded and it may be an electrical issue, or if it's completely a separate issue and it just happened to occur while being caged.

i am just now posting, because i've run out of ideas.here's a list of what i've done or replaced, in order.

New spark plugs, gapped to about .28.Coilpacks and groundsRe-timed to double check timingIgniter chipECUFuel Pump-Walbro 255FPRInjectors/injector sealscoolant temp sensor

the next thing i'm gonna do it pull the engine harness and go through it. i'm running out of ideas and am really hoping someone can help me. i'm becoming desperate.

thanks!