I have a 2013 LaCrosse 3.2L VVT engine with about 140k miles on it. My car was doing the same sort of thing and furthermore, the car would sometimes act like the battery went entirely dead (the battery was actually fine). Key would get locked in the ignition wouldn't start...bad news. The solution for me was: 1.) Clean and tighten all of the ground terminals around the engine bay. You can easily find and get a nut driver on about six ground terminals. 2.) Confirm a good battery and battery connections. 3.) Verify that your red, positive battery cable is all good. (Mine was hot to the touch, IE. too much resistance, so I just replaced it with an AC Delco part made in Mexico. It's was a short, 4" red battery cable.
Again my car is a 2013 LaCrosse Leather 3.2L VVT. These types of electrical problems, with this type of car, have been well documented in this Forum. Definitely do some TLC on the electrical terminals! Faulty ground connections caused me a lot of strange DIC messages, failed starts, etc. But there was actually NO electrical devices, sensors, PCM, ECM in need of replacement in my case. Hope this helps.