[Benram2500]

whenever I am driving and get up to 40 mph, I feel like I am losing power and start to get a lag. Any ideas of what may cause this???

 

[blueshadow2]

turbo going bad,does it hold boost before you hit 40?, either that or you have low oil pressure or bad/sticking injector(s) that would be my guess

 

[Rustin]

whenever I am driving and get up to 40 mph, I feel like I am losing power and start to get a lag. Any ideas of what may cause this???

You have an ISB? Lets start with the basics. When was the last time you checked you fuel filter? I would scan the truck for codes because you have an ISB that is electronically controlled. If everything is fine with the fuel filter and ECM after that. I'm guessing that you "Might" be having some sort of a fuel issue. I would then check your fuel pressure after all of the easy stuff has been eliminated.