Underboost

Has anyone seen a loss of boost occur due to a leak at the valve cover or is this not possible? So, we would be looking at diverter, map, actuator, hoses, N75, most commonly? PD motor. Thank you in advance.

No, a valve cover leak won't cause a loss of boost.

A loose elbow to the intake manifold can appear like a valve cover leak though...

Check all hoses and connections. Common fails are the elbow to the intake and the S-shaped hose off the turbo to the front cross-pipe.

I would start from the vacuum pump, since the N75 is actuated by vacuum.

Thank you for your replies, gentlemen. I have checked those hoses as I understand they are 1 and 2 on the list. Replaced lower hose less than a year ago because of rub through. Got P0299 code after hard acceleration to vary rpm input in engine. Was hoping I popped or split a hose as a simpler solution. Will keep looking. Thanks.

In addition to checking the hose condition, you may want to do some vacuum checks at various points. Start with the vacuum pump, connect a tee with a gauge right at the pump, see what you got. The line to the actuator will also help.
There should more thorough instructions for these checks somewhere.

Thank you for your input.