Chugging on a 1996 Chevy Lumina 4 door 6-cyl 164,000 mileage

I am having a chugging problem on my 1996 Chevy Lumina 4 door 6-cyl 164,000 mileage.

It was fine until last sunday. It has been cold here for a while but warmed up to about 23 on Sunday. When I drove my car it was fine for about 20 minutes, then on the way home, everytime I slowed down and completely stopped my engine chugged and then shut off. This happened 4 times in a row within a 10 minute time frame.

When I got it home I let it run in park and it did not turn off. I decided to get it looked at so I took it to a place. They did diagnostic tests on everything engine related and found nothing. All they said is that the coollant injection was slightly leaking and may need repaired in the future.

Today when I picked it up and drove home it was fine. However, everytime I get down to low mph the engine seems on the verge of shutting off. Also, when I parked the car today I let it run and it shut off after about 1-2 min. Then I restarted and it was fine for about 10-20 sec. Then it starts making what I'd call a reving/surging/chugging sound and shut off. I restarted one last time and it did the same thing.

I think if I can get it driving its fine but when I slow down, stop, or park it has this chugging/shutting off problem. Again, I took it in and they said it had no problems. I am thinking of taking it to a dealer and having their mechanics look at it.

Any help or advice would be greatly appreciated.

Thank you