Tons of black smoke, after driving.

When I first start it is normal, very little black smoke if any, after 30 minutes of driving or so (city). I feel like there is NO power and there is tons of black smoke. It starts clearing as it climbs rpm's and as soon as it shifts it is right back to the "bogged" state.

It is a '98 k2500 it has a 3" dp with a 4" exhaust. That is it. Also no gauges at the moment. That is next. It has 75,000 miles on it.

Any advice on how to clear it up. Also, it didn't occur last winter. On colder days it isn't near as bad and when the AC is on forget about moving after 30 minutes.

In my very limited experience it would seem to indicate no or very little turbo boost, check your vacuum pump and or electronic wastegate.

Very likely a turbo issue. Mine suffered a similar (but not identical issue). I think my problem was caused by the heating of the turbo bearings, causing them to expand and bind on the impellers, but I have a non-waste-gated turbo on my AMG 6.5L TD. New Turbo is on the way.

How would I go about checking this issue and if it is one or the other, what is needed to fix it.

Sadly, I (and the techs from Peninsular Diesel and Borg-Warner) have no way to test the issue. My engine is under warranty, and that, and the curiosity of Peninsular and B-W means they're sending a new turbo. There are no indicia of problems on the old one, sitting on my workbench...

But your issue does sound like mine in some ways, in that cold, the rig works like it should, but heated, not.