Engine cut out during hard pullls

More info would be helpful. What do you mean by "cuts out"? Turns off altogether? Stumbles and loses power?

all the idiot lights turn on and the engine is off.
one tidbit, there is a known back pressure issue
with the existing turbo. that's why I'm only
hitting 330hp at the wheel - to be replaced
later this summer.

Something harness related, either a main hot wire or ground is becoming disconnected or shorting…

Check the alternator harness and battery cables/terminals, is your battery even tied down?

Yes, the battery is tied down - I'll check the other things you mentioned. I'm also wondering is something is triggering the ECU to turn the car off?

I don't think there is a function in the ECU to just turn the car off.

I was thinking in a critical situation whereby you run too lean or rich, perhaps it might?

Nope, these ECUs are old and dumb. They would do their best to keep things safe, but they would just let your engine kill itself if they can't keep up.

I'd the tune was working fine before then it's definitely mechanical or electrical

The car has been worked on for the past 10 years, I just had it tuned, for all intense of purposes, for the 1st time last fall - thus I'm driving it 'really' for the 1st time with all the mods. I don't really have a baseline to compare it to, so perhaps I will go off the assumption it's probably electrical, since the ecu from what I'm told won't cut the engine if it detects a critical state.

Good to know, LOL - thanks.

If you're having issues it could be the tune if you just tuned it then. The map and other settings can cut out fuel and also cause a bunch of other issues.