All in the negotiation.
I am still running the tires it came with on the factory 20s. For the track I run 17s. Nittos in the front and M&H drag radial in the back. Works decent, best 60ft so far is a 1.8XX. Still on the factory converter.
Got her end of 2017 for Christmas.... my 2018 Silverado black edition. I got pretty lucky with mine. Flex fuel, leather seats and spray in bed liner from the dealer. Ran a 14.5, got her down to a 13.5 ??