Is yours and older 12v Cummins? Unless you have a turbo with variable geometry, you are going to get smoke out of a Cummins on the low side until the turbo spools. In the end, more boost is the solution to black smoke.
It’s a 12 valve. You must be correct about the turbo. I can feel the power come on as the turbo spools up in 4th and 5th. The truck really accelerates.