[Excaliber]

Well injector cleaner can't hurt and might help. But for some reason my gutt tells me (based on your symptoms) it's not injector trouble. I'm still suspicious of fuel pressure or the fuel pressure regulator (which has a vacuum hose on it. is it nice and tight)?

Fear not about the O2 sensors, at that kind of mileage it was a good call to replace them anyway. What about that fuel filter?

Edit:
OH!! Just thought of something. Clogged up catalytic converter OR internally collapsed exhaust pipe would give symptoms MUCH like you describe! By pass the exhaust if at all possible for a "test drive". I once had a Buick (customers car) with an internally collapsed exhaust pipe that took FOREVER to diagnose. It was real close to where it bolted on the exhaust manifold, the metal inside all folded "inward" and restricting exhaust big time!

The "clue"? Manifold vacuum would be steady to a certain rpm and then DROP like a rock when it hit just the right rpm!

Ernie