Did you ever shut off car and restart? Was the problem still there? I've seen several Chevys with this problem most of them had a p1516 code, anyways the reason it loses power is because the computer sends it into "limp mode" because it sees a glitch in throttle position sensors and can't decide what the driver is doing with the gas pedal, (as the throttle is fly by wire) anyways the theory is better safe than sorry and they program computer to give just enough juice to make it home or to the end of a hook. Good luck with that, this is one of Chevys treat innovations.
It was definately in LIMP MODE... I did shut it off once at the first place, restarted it and it did the same thing... after sitting for a while I started it to line it up with the flatbed it had toime to cool off and it sounded fine but I only idled my way over to the truck... The check engine light and warning still showed up.