I dropped my Dad's LBZ off at the dealership today for him, he has:

Leak in the front diff and Transfer case,

CEL, been on for a while, he works too much to take it in. This started about the time he had an AstroStart installed, not sure if it is related or coincidence.

Needs glow plug recall

Has seen black smoke pouring out the exhaust while cruising down the freeway. It is intermittent, may be related to the CEL.

Hopefully they do a good job, his truck is meticulously clean.

I asked them for all of the codes regardless of whether they fix it or not.

OCDUNE

Truck is done, they replaced some seals for the leaks. As far as the CEL, tech claims there was no codes, and that there is a bulletin from GM stating that in the case of CEL with no codes, there is a software update to address.

OCDUNE

I got a cel after installed my AstroStart because one of the white wires got unplugged from the main unit when I was mounting it.

What did you do to clear it? I believe that he tried unplugging the batteries overnight.

It went away after a few cycles of the key, undoing the batteries doesn't work on anything after 2000 IIRC.

I have same problem for past two days black smoke pouring out the exhaust while i'm on freeway, the problem is intermittent.

Have that issue been clear for you?

What is the astrostart? sorry but new to Chevy...

It is a brand of remote start.