93 coug dies when idle

:crying: My 93 cougar dies when idling at lights/stops for the first 10 minutes or so of driving. It also, sometimes, has trouble upshifting and downshifting. Only 75k miles on the car, trans was replaced because we thought that was the problem but it still dies.

I remembered that it only has one catalytic converter (though it's supposed to have 2) and someone suggested that this may be the problem. Any thoughts?

Thanks in advance!