Combines 670T rpms

Ok, you have low power WITH smoke and ok injectors. (injectors are rarely a problem unless a dead miss is involved) Barring a mechanical problem such as dragging brakes, this indicates either retarded ignition timing or low turbo boost. At full load you should have 16-18 n intake manifold pressure. Check the plugs in the intake manifold to see if any have unscrewed. Pull the intake sleeve and inspect impeller in turbo. IF it is a AirResearch a little play is normal but the blades should not touch the housing. Check the timing as well and look for slippage at the mounting bolt holes on the old style pumps. Newer pumps have slots in the drive gear and three bolts to adjsut timing.

When the injectors were done, were they put in, in the right position.

Tbran when you say manifold presure do you mean boost presureIJ Mine runs 7 to 9 psi on the boost presure gauge when loaded. I had the injectors rebuilt at midway diesel in Mandan, ND. and installed them myself, in another post one talked of installing them wrong, dont know what he means as the return line goes on the top and the rest of them have to line up or the return line won't fitIJ I replaced the injector because one was droolling. Found a few of the six were not breaking at right psi and droolling. Thank You.

Yes, the return line does face the valve cover, but on the N-6