95 deville 4.9 stalls, no codes, need help!!

I have a 95 deville 4.9, that only stalls in gear and only after a block or two. the car doesn't stall right away, and it doesn't stall with the pedal to the floor. it only stalls at a stop or at low throttle, but when it does you can start it again in park only. we connected it to a modis and it said that there are no codes present. could this be a bad shift moule or a computer on it way out. has anyone here had this problem, and does anyone know how to fix or atleast diagnos the problem. thanks

I have the same problem with an 85 deville with only 35k miles. We have tried everything we know. If you find something, let me know. Thanks.
Mike