Heat related problem

About a year ago my Dodge Ram v6 started missing shortly after starting but settled down after a few minutes. Now it runs until the engine is hot, starts missing and then stalls completely. When it cools it
repeats the behavior. Have replaced spark wires, dist cap, and coil to no effect. Fuel pump has proper pressure. Mechanic I sometimes use has no ideas. Any suggestions as to what to look for would be appreciated.
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Many years ago I experienced all these same symptoms in an 82 Aries K-car. I had every fuel and ignition related item checked repeatedly with no results. The final determination was that something had broken loose inside the catalytic convertor and would bounce around, periodically blocking the exhaust flow. When blocked, it would stall. After the stall, the exhaust pressure dissipated and it would run again ....until the next occurrence.
GrtArtiste
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