I have a 2011 Silverado 2500 HD crew LT. It has an LS 6.0. It seems to run out of power on the highway. Almost as if the timing is not advancing on hard acceleration. I was told to change the oxygen sensors and I will be doing that this week, but, what else coul;d cause it? Cam sensor? Crank sensor? FYI: The truck is immaculate and has 50,000 miles on it. Thanks.