I first found this thread,
https://chevroletforum.com/forum/1999-2006-gmt800-108/engine-power-reduced-light-17542/
and then a few others on the "power loss" indicator light.
Seems this is a known problem.

For those who have not seen this yet, your engine will drop to an idle and no matter how hard you push the pedal, it will not rev the engine. Shut it off and restart it, and it will be fine for anywhere from .5 to 500 miles and do it again, and again, and again.

While no one is sure of the exact cause, I've found the three most talked about fixes.
Accelerator pedal replaced.- These have NO cable, it's all fly by wire PCM controled.
Fan Clutch.- Chaffing wires causes a voltage drop.
Bad Crimp at TAC plug.- A weak crimp and sub-standard wire.

This rig, an '03 Trailblazer, has already had the accelerator pedal replaced more than once,
and last week I replaced the fan clutch.

Today it did it (power loss light) again.

So I call the local chevy dealer and find "PT1576 connector w/leads" is $154!
(this is a plastic plug with 8, 6" wires sticking off it!)
I found it at a local parts place for about $25 less.

I'll let you all know if this fixes it.
EZ1