ZDriver.com - Strange Issue...

I have a 1990ZX na with unique problem. Engine will not RPM above 2500. If I try to go above that, engine will surge as if I'm working the accelerator. Will sometimes break through and then accelerate/ run fine in general, though it may shut off momentarily (up to 2-3 seconds) while driving, as if I turned off the key. Never can predict when this will happen; car may operate normally with no problem! I'm original owner, always have used premium fuel, car has just over 120k on it. Dealer has had no luck in correction (I don't think they've a clue what they're doing, or much interest in helping.). Since the car runs well when in the right mood, and runs well up to 2500 RPM, I don't think it's a mechanical (fuel pump, filter, injector) issue. I think it's electronic. But I'd appreciate any suggestions. THanks.