What I found is that these newer cars have the voltage controlled by temperature. The voltage will change greatly from day to day, which obviously affects the power output of the radio that in turn drives the amp. The current truck I own (a 2012 Silverado) will charge anywhere from 13.8VDC to 15.1VDC (as read from an external volt meter) from day to day, and is considered normal. What I found was that I was continually adjusting the dead key for these voltage changes with the radio's variable...it was definitely not a set and forget deal. I've seen instances where I set a dead key that was perfect the night before, and grossly too high the very next day (that was a Uniden 76 running into a FatBoy 1x4).
While some amp/radio combinations could safely have the dead key turned down in the radio, I personally wouldn't try that with a driven amplifier (e.g. 1x4, 1x2, 2x4, etc.).