MLR19

I have a 99 Z-71 , 5.3L 4WD, 175000 miles. I have owned this truck for 3
years & I really like it. 6 weeks ago I drove it about 10 miles, no issues ran great as always. I was going thru the drive-thru at Mcdonalds, & it started idleing rough & would barely pull itself. I managed to get out of line & into a parking spot. I t died & I was able to restart it but it was randomly missing & would die. I finally left it & walked the 3 blocks to work. I called the chevy dealer & they went & got it. They called me an hour later & said it started right up & ran fine & they couldnt find anything wrong.
So for the last 6 weeks it has been running fine, earlier today I left it sit idling with the jumper cables hooked to my neighbors car, it started doing it again. idle going form 100 to 500, running eratic, dieing. It would restart
but kept dieing, no power, if I tried to give it gas, it popped thru intake & died. left it sit for 20 minutes , restarted it & it ran fine, so we left it hooked to his car, it died again in about 5 minutes.

Left it set 20 minute & it started fine & I drove it for 15 miles, no issues, it ran perfect.

I hate a truck I cant trust, anyone have any ideas where to start?

Thanks,, MLR19