1992 buick stalling problem

I have a 92 buick regal with the 3800 V-6 with 60000 miles on it. Sometimes at an idle the car will run rough then straighten out. Lately it will do this when I decelerate then stall and I have a hard time restarting it. When
it starts again it feels and sounds like its running on 3 cylinders then stall again as soon as I let up off the gas. This will go on a few tries then all of a sudden the car runs fine. It can run fine for a few days even a few weeks then it acts up again.3 mechanics and Nobody has been able to figure this out. I should mention that a year ago this was happening more and more and a mechanic blew the motor trying to duplicate the problem. I have since had a different used motor put in by a different mechanic and a year went by with no problem and now its acting up again. When the new motor was put in the mechanic told me that the PCM was way off and he adjusted it. This has recently been rechecked and it's fine but the stalling problem still exists. Any ideas what the problem could be and is it a common one?
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Well first of all there is no "adjusting a pcm", but any way, pull the egr make sure it is not carboned up and sticking open. Number 2 get to the ecm and do a tap test and see if the engine stumbles, also tap the maf sensor with firm rap from a screwdriver handle, see if this causes the engine to react, ideally for proper diagnosis this should be done while monitoring a scanner.

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TCC solenoid in tranny. Engine stumbles and stalls when slowing to a stop after warmed up and driving at a speed of over 40mph.
Have you driven a manual transmission vehicle? If yes, are you familier with how one feels when you forget to push in the clutch when coming to a stop? Like a bucking bronco then the vehicle stalls.
If the car feels like this, look to the TCC as the problem, VERY common, and usually very intermittent at first.

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