1997 cavaleir DTC P0171

Car runs fine except for a slight miss after operating temp. Has been reached. When you shut car off and it sets for a short period say 10 min. Or so it idles fine but when you accel. It want's to stumble, this will claer up all but the very slight miss in just a short time. You can take it out of gear when this happens and run at high idle and you can hear it clear up and put back in gear and will be fine till next short shut down. Appears not to happen after long shut down periods such as 30 min. To hour depending on outside temp. Have checked for vac leaks and have not found any. Fuel pump, filter, and fuel pressure reg. Have all been changed about 8 months ago, this problem came about a month after that work. Can you lead me where to look next.

Thanks,
rjg71