I know these engines are GDI, I have a 5.3, 2015 Yukon XL. I also have a Kia Optima that is GDI. I had to take off the intake to clean all the crap off the intake valves, it made a noticeable difference in how the car runs. The Kia dealer obviously offers these types of services with chemical cleaners and what not, does GM offer anything similar? I called the dealers in my area, they claim to know nothing. I know these things will need cleaned eventually, I just want to stay on top of it. Has anyone cleaned their intake valves? If so, how? Thanks!