black soot means too much fuel.

To un-stick the oil rings....

Block off the radiator
Run the engine until the engine is running HOT.
Pour a half can of tranny fluid down the Carb. while the engine is running.
This can be done but you need a lot of throttle and pour slowly.

The last half of the can Hold the throttle wide open and dump it in.
Let the engine set for 48 hours.
Clean the plugs and restart the engine.

It is going to smoke like crazy for a little while until the extra Tranny. fluid is burned off.

Replace the plugs and drive the truck.
The ATF will break down the carbon and clean out the gunk clogging the oil rings, and let them work like they use too.