OK, so your fuel trims are very high. The computer is trying hard to make the mixture richer, likely due to the high oxygen concentration detected at the exhaust.

checking for EGR or exhaust leaks would be a good idea.

 

My truck is an '01 and not flexible at all. Though hard to find, I but ethanol free when I can but typically have to weather the "may contain up to 10%" nonsense.

 

Thanks, I'll do that first and let you know what I find out. I last replaced the EGR valve about 50-70K ago as it was a culprit for bad start/idle years ago, but I think it wasn't cold exposing the issue at that time, it was just fouled quite bad.
Since it acts up especially when cold, it kinda makes me think it might be the tube in lieu of or with the EGR valve as the contacted metal when cold and expanded when hot just runs inn my mind. Can I check this with spraying the joints when cold startup or am I missing the actual testing for the EGR tube?
I guess I can check the connections and pull it to look at the internals, check the resistance between the EGR valve terminals, etc. But probably this is an old "throw a new part at it" kinda thing 'eh? I have had other Chevy guys I know with newer and fewer miles speak of replacing the EGR lines from the manifold as well as they seem to develop breaks and cause leaks which throws off the signals and in the end the computer alters the fuel air mixture.

 

No. Use a smoke machine

 

If I had one I would, but alas.....

 

https://m.roadkillcustoms.com/free-l...ools-services/

 

I checked, no one local rents them...

 

Do you like cigars?

 

Haha, I have smoked a few in my life, but I found a shop with one and I know one of the guys so I went over and we used it at the end of a day. It showed a leak in the intake gasket on the passenger's side. I now have the gasket set and I will start the repair today. I'll advise when complete and I run her a while..

 

Get a smoke machine from Amazon, they are cheep. I bought one to test vacuum leaks, been wanting one for years.