So to revive this old Thread, here is an update for anyone interested.
I took my suburban to the GM expert independent shop.
The did not address my concern, they sold me a Direct Injection cleaning and Injectors cleaning.
Not that I mind, as I wanted to do the direct injection cleaning anyways.
This did not change any of the smell.
To recap if some of you don't want to go back to all the different pages and bogus info I was given or thought it could be, this is where I stand on this of of right now:
At every start upt, cold or fully warmed up engine: the truck rear tailpipe smells super rich.
as in raw gas strong smell.
I am taking the truck to an actual emission place who is going to hook up HP tuner or some diagnostic to look at the tables while starting it tomorrow morning
Recently, I had a 19 loaner with the 5.3 and I could have sworn that that brand new unti also does the same thing, smells really rich at startup and idling.
My particular smell stop once I get going and then stop.
Maybe its something GM designed (poorly) into the truck, my truck is all stock with no lights on the dash, everything indicate that I am running in good condition.
I will update with that shop finding.