I have a 2004 Sierra 2500HD 6.0L 4X4 with 42,000 miles. When at speed (starts around 20 mph) the truck as a light surge. Feels as if the accelerator is being pushed and released very lightly. This is also happening when using cruise control. Dealership had my truck for over a week and has no answer. They do acknowledge the problem. HELP!

 

2004 is drive by wire right? Maybe an issue with the control module on the throttle body. Just a guess.