Yeah at constant speed and removed silencer ring??

Sounds like it could be the apps. Try resetting the apps first. If that doesn't work follow the testing procedures on this link VP44 Diagnostic I have read about 3rd gens that had surge probs where they reinstalled the silencer ring and it solved the problem so if you still have it you might want to put it back in and see what happens.

I will check out the link I am new to diesel so it is a learning exp for me!

surgen 24v !!
 

had the same/simalar problem,took me 2 weeks to nail down,turn out to be a suction problem
at fuel modual.made my boost gauge go nuts cruising down highway.do you have a fuel psi gauge? wound up getting new fuel modual hope this helps.:humm:

I am wondering if it could also be a huge vac leak?? I just got a kit from gould to fix my enormous oil leak in the vac pump???? Not sure yet thanks to all