When sitting at an idle, my 6.2L turbo has a slight rev up rev down rev up rev down and when i slam on the pedal, it has a cough right before it hits idle speed. I already have the fuel turned yp, any suggestions?

How does it start? Is sounds like you could have an air leak in the system.

not sure the year of your truck but the lift pump could not be working at idle, I had a similar problem

thats your enemy air. when it gets in the system it screws with the idle speed. i had an airleak untill i changed my fuel filter and the engine used to idle all over the map. it would idle smooth then rev up to around 1700 on its own then go down to idle then do something else spooky.