UPDATE Turbo boost check stop engine CAT C7 error back

What's odd (to me any ways) is that it does on flat ground cruise set to 55 mph 10-12 pounds of boost randomly. It will be fine for 10-30 minutes then it spikes to 35 on the screen. I'm reading up on causes and will be testing the waste gate when I get home.
Also going to check my slobber tube as I read that can cause it.

Also curious why a new turbo costs $4000 when they are on EBay for $500 brand new.