Again, not enough info here. Telling us it's "well maintained" doesn't help, I don't know how you maintain or with what. Need specifics. No turbo power? Meaning the turbo is shutting down? Do you have a boost gauge on the truck? Can you hear the turbo? Are you getting any black smoke when this is happening? Any other symptoms? Have you tried scanning for codes? Even if the check engine light is not on, you can still have codes, I would start there personally. The turbo impeller is not spinning? As in it's not spinning when the truck is running or you can't get it to spin when the truck is off or what? Shut the truck off, pull the intake, try moving the impeller around and see if the shaft is loose in there. It SHOULD have some side to side play, but NO in and out play. Make sure the impeller blades are not hitting the compressor housing.

This should help in getting us the info we need: https://www.dieselbombers.com/ford-p...questions.html