What's throwing me off here is "The check engine system was disabled and cannot be read"
I would think the first step of getting it fixed would be to repair the check engine system. Now, I'm not up to par on the computer system in your truck, but I can't say I ever heard of just disabling the check engine circuit without shutting down the rest of the system as well.
However, the issue your having is somewhat common on those year models. More than likely the intake gaskets are leaking. GM recommends using they're replacement gaskets that are upgraded thickness.