my 2019 LTZ also didnt power lights at first. Even though the trailer brakes worked. Later it said that the trailer was disconnected. I changed the profile on the 'car hauler' and
removed backup lights. I dis and reconnected the 7-pin connector then 'added' a trailer. The truck prompted me to test the trailer lights and it looped through testing left, stop,
right lights and sure enough the side markers were on as well. Havent tried it again but will. dont recall now if I set it to tow/haul mode. Neighbor said his 2011 ran used to report 'disconnect' and 'connect' while driving
all the time.