Loss Of Power

First off, do you have a boost gauge? If so is your boost low and are you having boost lag? If so, go buy some pvc and a couple fittings. Disconnect the discharge off the turbo and pressure test the rest of the system to about 20psi and use soapy water to chew I for leaks everywhere especially the charge cooler.

If no boost issue, could be as simple as dirty primary fuel filter.
I assume you have no check engine light on while driving?

 

Especially check the cooler inlet elbows. They crack

 

And if it’s leaking enough to where you are losing noticeable power, it will be a leak where you won’t need soapy water. You will definitely hear the air leak without having to listen closely

 

VPODS?

You said it’s a 14l Detroit right?

 

CAC pressure test.

What boost pressure are you building at load right now?

Are you sure the 12.7 turbo is compatible with the 14l ?