OK, heres the deal...

my girlfriend has an 84 Z28 that she had converted to TPI a while back. just recently she started having "issues" with it. it started off as just a high-low, infrequent idle, but now she drives it down the road to work and it'll just shut off. it doesn't happen all the time though. she went to lunch at work and her car wouldn't start back up after it stalled in the parking lot, but when i went back to get her....low and behold it starts up just fine and the car made it home with no problems.

i haven't really dove into it yet, but i do know that it's not a vaccum leak. i did check that!

the only other things i can think of are:
fuel pump? but you can hear it engage when you turn the key...
fuel filter? maybe clogged and not letting enough gas through or maybe caused a temporary vapor lock? not to mention it's an old car and probably has some crap in the tank
IAC sensor?
TPS sensor?

I'm really lost on this one, and i'm gonna go bald from pulling my hair out if i don't do somehting about this quick! she keeps nagging and nagging for me to fix it, but i'm not gonna just go throw money into a bunch of parts that i may or may not need and that not be the problem. any suggestions come to mind?