I have a 94 k1500 it ran fine when I got it a few months ago but I started having problems. I would get this rattle noise under acceleration it sounded like every valve wanted to drop out of the motor along with no power and a tone of black smoke. someone told me it could be an egr problem so I unhooked the vaccum line and caped it off it ran OK for awhile but now its back along with run away rpms and a lope idle. what really gets me is it runs fine when I first start it until it warms up

 

You need to check the vacuum and boost system.
Boost is vacuum activated from ECM control.

Or buy or build a "turbomaster" and adjust properly.

A boost and EGT gauge should b mandatory install items for all 6.5TD's.