90 Mighty Max 3.0L Revving?

Hello all! I have a question, I have a 90 Mighty Max 3.0L and I'm having an issue with it revving.

When you start it up it just idle's high until its warm but once its warm it just starts revving from 800 RPM to about 1500-2000.

Now I have already replaced the Idle Control Valve twice and that didn't do anything. I replaced the distributor, plugs, and wires as well and no change. And we also had the ECU rebuilt (for a different reason) but still no change.

I'm looking at replacing the Throttle Position Sensor next but instead of throwing more parts at it I want to see what you all think. Should I do it or is there something that I'm overlooking?

Thanks in advance for all your help!! I appreciate it.

-Chris

Any ideas? I'm thinking it's not fuel related caused it only does it at idle. It's also idling higher than normal.