I've had to do a whole bunch of work on my 2015 LT lately (replace all of the cylinders and fuel injectors on bank 2; replace the transmission; and replace all of the spark plugs and wiring.) Now the dealership is telling me, after the check engine light is still coming on and the vehicle is shaking while idling, that the catalytic converter needs to be replaced for $3500. However, they did also tell me that a muffler shop could cut it off and put on a universal catalytic converter for cheaper. I've called a couple of shops to run this by them, and one said to me, "You know it has 3 catalytic converters, right?" Anyway - is that accurate? I've done some Googling and I've seen some references to multiple catalytic converters on other GM vehicles, but nothing specific to a 2015 Tahoe.