Welcome to the Forum from NH.
Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.
I hope that you will become a participating member in the Forum's discussions.
Pics of the truck, please.
I cannot personally assist you with your issue, but other members of this Forum much more knowledgeable than me in your generation truck will chime in. Lots of GMT800 truck owners here.
To assist folks is assisting you, please go into greater detail on exactly what you do and exactly how the truck responds, or doesn't respond, at the point of the issue's beginning.
Was any work performed on the truck recently?
What did you use to scan for codes? A quality bi-directional scanner, or a cheap scanner?