I own a 2014 Silverado LT 4x4 double cab V-6 with a build date of June 2014, I do not have adjustable pedals, my pedal bracket flex is insane.
I noticed the lag in accelerator pedal tip in response from my first test drive of my new Silverado from day one with 18 miles and still have issues at 900 miles.
This design problem isn't going to correct it self and will only get worst from usage.
I don't know from reading all of the threads and posts which 2014/2015 build dates and models are impacted, but I think once owners can see the bracket flex in their trucks they will only then understand the issue.
This issue seems to be for the fixed pedals only and not for the optional adjustable pedals.
Happy 2015 !!!