I have a cheaper OBD2 reader, I've scanned it multiple times including the day it stopped running but there haven't been any codes stored which is what I found to be strange was when the truck just shut off it didn't throw any codes it just thinks everything is fine. I will check for spark when I get home today and let you know what I find.

 

Okay new development, I do have spark and with the use of a little starter fluid I was able to get it to fire off, only for a couple seconds though. So it seems I'm not getting fuel to the cylinders, but my pump is running and it seems like my rails have decent pressure, it would lead me to believe that my injectors aren't cycling but I don't know what would cause that.

 

Well, I guess the next step is to figure out how to test an injector, and trace it back. Hopefully someone else can jump in here and give some advice, as I'm not going to be able to help much today.

 

In my '93 Sub, a failed ICM caused this 3 times in 350k miles. No idea if this applies to your vehicle, but easy and not expensive part to change in mine

 

I looked into that as a possibility, it appears on the lm7 5.3 the ICM is integrated into the ECU, so I'd have to replace the ECU.

 

Before you go disassembling anything, get hold of a fuel injection system pressure gauge and see if your fuel pump is working properly. The Key On Engine OFF fuel pressure specification for a 1999 Silverado with the 5.3L engine is 55 - 62 psi. With the engine running it will be about 5 - 7 psi less. Just because you hear the fuel pump spinning does not mean it is pumping fuel. Also, the average current draw for the fuel pump is 10 amps.