Issue with idle after tune

[ncsurveyor]

I recently put a 6.2 L94 with 4L80 in my 68. It ran great with the stock tune from PSI but I had a check engine light on. So I took it to be tuned a couple days ago to see if they could get the CE light to go off. Now on startup it idles really rough for the first 15-20 seconds before settling down and idling smoothly. It with continuously rev up and down between maybe 500-1000 rpms. I’ve been back to the tuner and they can seem to fix it no matter what they try and I finally told them to just put the stock tune back in it, which they claim they did but it’s still doing it. I suspect they accidentally saved over my stock tune and weren’t able to put it back in because I could see on their computer the stock file had a more recent save date than my first day there. Anyway, does anyone have any ideas on what would cause this? It seems to run fine, other than the rough idle at startup.
I was able to get PSI to email me the stock tune and I plan on flashing it back to the computer on Monday. I just hope that fixes it back to running and idling smoothly.