93 s10 4.3 ALWAYS starts great no matter how cold outside but once in a...

...great while idles funny and dies? No matter how cold it is my truck starts fine. In the last three weeks it has died twice while warming up. The first time I wasnt there to hear it die but the second time I drove to the gas station a mile away and while I was inside heard it idle high for a second, then idle low..it did this on and off for about 20 seconds then died. Started up right away and hasnt given me a problem since. It appears that this only happens when the truck sits a day or two without being used. Again, it starts FINE every day. It never did this before I replaced the battery and yes the computer has been reset. Doesnt throw any codes. Any ideas? Thanks in advance!