1990 Buick Lesabre engine stalling while idling after runni

My car will run good on the highway until I get somewhere and it's sitting idling. It'll start running rough and stall out. Sometimes it'll start right back up sometimes I have to let the car sit for awhile. I've replaced o2 sensor, throttle position sensor and idle air control valve fuel filter still doing same thing I'm stumped! I do a driving mail route it'll start out good then about an hour into the route it starts stalling out. Help.