New Pickup, 500 mile/15 day warranty, What all do I check?
 

I picked up an 03 Duramax, with replaced injectors, new transfer case, new front hubs, new water pump and 129K miles yesterday.

I checked, and I can't tell if there is blow-by for sure or not. I see oil vapor at the fill cap when I run the truck about 15-20 miles on the freeway, but it doesn't really seem to puff out and if I place my hand over the fill area, I don't feel any pressure build up.

My main concern when I got home, I found the air filter life monitor had been knocked off. The area where the grommet goes is still very clean compared to the rest of the out side of the airbox and the truck was serviced at a dealer 4k miles ago.

I assume it was knocked off recently, maybe when they were cleaning the engine bay to put the vehicle up for sale, but not knowing for sure and having the supposed warranty, what all should I check?

Lastly, I drove the truck home last night, about 225 miles, the truck seems to run smooth and no smoke from the exhaust according to my wife that was following me.

Thanks in advance and if there is anything else not engine related that I should check feel free to mention that also.

Sounds like you pretty much covered the basics ... I would have them replace the filter-minder .. dont wanna suck any junk into the engine or turbo ...