Runs for a few minutes then sputters and shuts off

It started where I could drive it for about 10 minutes then it would lose power and shut off. Later that day, I figure drive it to a local shop, now it runs rough and would only run for about 30 seconds and shut off. (Multiple misfire code).
The shop has looked at it but they are stumped.
I'm starting to lose faith in the shop as they have been looking for 4 days now.