I have a 2009 Chevy Silverado 2500 HD 6.0 l. When I'm driving down the road and if I need to accelerate real fast or want to speed up when I press the accelerator pedal the truck downshifts and gets stuck on a certain RPM and it actually slowly decelerates. I am leaning towards the fuel pump and fuel delivery like it's being starved but I really don't want to tear part into the gas tank to get to the fuel pump in case that's not the problem. If anybody has had a similar problem or knows what I'm going through please help thank you