Took the truck in for a software flash to fix P0191 code with a check engine light. They fixed that but now it won't fast idle. Has this happened to anyone else? I imagine it just has to be re-enabled but I'm annoyed that I have to make another appt. and burn fuel and waste time to go back there.

 

Yup, the reflash that the dealership did disabled the high idle. It happened to me last week, I took my truck in for the hard start/white smoke reflash and it disabled the high idle. I always check it when the dealer messes with the ecm, and when I did before I left the dealership it didn't work. Had the tech hook up the tool and it showed that it was still enabled, so he disabled it and then enabled it again and it worked. The tech didn't understand why it happened.