while sitting in drive thru, truck stalls while in park. started right back up but only a minute later stalls again. started right back up and drove home fine. where do i start the trouble shooting?
I would hook up a scanner or code reader and retrieve any current or stored fault codes
I don’t know what model year you have, but based on the symptoms, the culprit could be several things, such as a crankshaft position sensor or an idle air control valve
Please . . . do NOT go out and replace these things, just because I mentioned them
At least not just yet 
What year truck?
Tester
will it read even if there are no warning lights on?
2010, had the heater core hose replaced a month ago
If the engine control module has stored fault codes, the scanner will retrieve them, even if the check engine light isn’t currently illuminated
Try banging the MAF sensor with screwdriver handle and see if it quits. if it does it may be a bad MAF sensor
A dirty electronic throttle body can cause stalling.
Tester
Ask shop to measure the idle rpm, compare to spec. I’d guess the spec is around 700-800 rpm warm idle.