First, don't panic. :)
Second, educate yourself on what questions to ask your mechanic. (you want to avoid rip-offs, and asking good questions helps with that, so do some google and youtube searches on what to ask your mechanic)
Third. The first thing to find out, when they call to say what's wrong is......
"what is my car coding for (what code is in my cars computer)"
The shops response might not make any sense, but write down whatever they tell you. They should be able to give you a number like "P0705" or P1138. You might not know what the code means, but it lets them know you aren't totally clueless about your car. This discourages them from dishonesty, at least a little bit.
It's fairly common for newish GM (Chevy) vehicles to trigger reduced power mode/check engine/service traction control lights all at the same time, and for only ONE problem. While its possible that your car has experienced multiple systems failures all at once, it's far more likely that one problem is causing all of those lights. And it's not very likely to be the PCM. In fact, it's common on newer GM (chevy) to see all of those lights, and simply need a throttle body cleaning. (I know that sounds unbelievable, but I work on many different types of cars and I see very few PCM failures, and many times multiple warning lights track back to one basic problem)
And, all that said, I don't have any way of knowing what's wrong with your car, but I think you are "jumping the gun" by planning on replacing the PCM.
Your post said that "everything else" was ok, so don't be afraid to drive your car to a different place for a second opinion, if you feel uncomfortable with the diagnosis you are given at the current shop. Beware of shops who claim that your vehicle is "unsafe" to drive away in, especially if you drove it to their location safely. If they make this claim, ask some tough questions, and have a clear understanding of the problem and the danger, before you either drive away, or decide to let them fix it.
Hope this helps
had same problem with my 2011 impala pulled codes found right front bearing pack abs sensor was bad changed bearing pack , problem went away for one day and return , turns out wire harness from the computer to the connector of the bearing pack was giving ,off false reading
