1998 Dodge Avenger RPM drop and occaisional stalling

Engine Performance problem
1998 Dodge Avenger 6 cyl Front Wheel Drive Automatic 250k miles

My car has been acting up for about a year or so, Ive done alot to try to get it to work properly. Spent 1000$ for a tune up with all of the symptoms in mind, regular use of fuel treatments and injector cleaners, and now im down to replacing parts.

Anyway, here's the scenario:

Going about 30 km/h or less when very minimal pressure on the gas is applied. Taking pressure off the gas to stop, coast or even accelerating in between traffic, engine RPMs drop right to about 100 or so and then sometimes it stalls and sometimes it recovers. Also happens in reverse. Another symptom is going about 60 km/h steady, the car will feel like its jolting back and forth, also with minimal gas pressure applied.

Recently, We have cleaned the Air Idle Control and the entire Throttle Body, then replaced the AIC(not convinced that we calibrated it properly we got a whole different one from Pick and Pull), tried to replace the TPS but none of the models fit properly, so Pick and Pull :P got a different one, got a new PCV valve, and replaced gasket which was ripped in two places that was apparently replaced and paid for during the tune up. The Intake manifold gasket. This weekend I grabbed a whole different Throttle Body from a 98 Sebring, which is the exact same engine. Thinking the throttle body may have been worn out. But still the same results. :(

What do you suggest?