Stumble or bog

I have a 90SC auto that does not accelerate smoothly when doing so in a gentile manner. If I accelerate sharply, it does so in the proper manner. In the old days using a carb, we would call it a bog. I have replaced the IAC and the TPS and neither had a positive effect. I also cleaned the mass airflow sensor with brakekleen. What do I do now, I find this quite frustrating. When the car is up to speed and in OD, 60mph or so, everything is fine. This stumble or hiccup is really irritating. Please help if you can.

Maybe a bad fuel pressure regulator? Bad cam or crank sensors? Bad cam sensor synchro? Failing harmonic balancer? Slack in timing chain? Chain jumped a tooth?

If the timing chain jumped a tooth, or was slack, would not the car act funny all the time, not just when accelerating in a gentle manner ? Also, could I not rule out the harmonic balancer for the same reasons ?

Fuel filter?

Have you changed your fuel filter lately?

Tom

No, I plan to get a new filter tomorrow or Monday. That crossed my mind, thanks.