1994 Dodge Stealth keeps stalling at idle when warmed up, why?

I have a 1994 Dodge Stealth (base model) with a 3.0 SOHC V6 Mitsubishi engine and automatic transmission. Recently, my car would often stall when idling after it's been fully warmed up. It runs fine when it's cold, has no
problem starting up, runs smooth and has plenty of power when cruising or accelerating, and I have not noticed any drop in gas mileage. But after I've been driving it for about 10 minutes and the engine's reached it's full operating temperature, when I come to a stop the engine starts stumbling and running rough, and the RPMs drop and it stalls out. I thought it might just be a case of bad watered-down gas, but after 2 tankfuls later from different gas stations and 4 bottles of Drygas (fuel drying additive) it's still doing it. It hesitates and stalls even when I slip the transmission into Neutral or Park. For the time being, I've been able to keep the engine from stalling by turning up the idle screw, but it still often runs rough at idle so it's not a permanent fix. Also, my "check engine" light does *not* come on.
Maintenence info: Within the past 20,000 miles, I have replaced the fuel filter, timing belt, spark plugs, plug cables, distributor cap and rotor, battery, and just recently the air filter.
Thanks for any tips!
- Logic316
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-SP
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