stang keeps shutting down?

[JM90GT]

Some of you may already know but I burned up the alternator last week, since then my car will just shut down while at idle. It doesn't happen every time, but it has done it about 5 or 6 times. Always at a stop and once it had like this power jump. I mean the car wanted to just take off.
Now as far as the dying goes, the new alt puts out 80 amps vs. the stock 75. and the pully is bigger which makes the alt turn slower. (correct?) This should create lower amps at idle, right? Now the car almost acts like it is cold, this happends in the morning when I leave for work, and some times when at idle at a stop. I can tell some times when this happends that the car is going to dye and just pumping the gas will keep it going. Other times it just dies with no warning. Any ideas?