Looking for a diesel guru

I drove truck for years, and a few of them were heavy haul/oversize. I have plenty of experience and a ton of miles and fuel burnt under my belt. I had a kenworth with a cummins 400 and 13 speed for my last truck. I drove that particular truck for 2 years almost trouble free. One time, it started losing quite a bit of power, and when I stopped and got out it was smoking like a freight train from the 1800's. Made the truck completely un-driveable, it wouldn't boost at all. It ended up being the wastegate on the turbocharger seizing up, not allowing boost pressure to build and be forced into the intake. They replaced the wastegate and the truck ran perfect again. I seriously doubt it's an injector or anything else.