Vehicle is an 03 Silverado 1500. Engine is Vortec 4300 (LU3?)

I have an OBD2 reader and am getting the code P0200 followed by 01/02 and 03/04.

I have been spending a few hours looking for what the last 4 digits mean but cant figure it out. Is it cylinder 1 2 3 and 4? Either way, I am having trouble figuring out if the issue is electrical or maybe the injectors themselves?

I am looking for ways to test and/or fix!

I drove somewhere and then parked for 4 hours, when I went to leave is when I noticed the problem. I believe a cylinder isnt firing. It feels underpowered and shakes at higher speeds.

Thanks all.

Also, within the past year, the truck has new plugs and wires and fuel filter.. if that helps.

 

Got it taken care of.. neighbor works at GM and had a better computer diagnostic. Narrowed it down to the #3 injector. Just ordered parts at napa.