4.3 sending smoke signals, need help

i had a phone call tonight from a friend that is having problems with his truck. he said it will start and run fine but then start to miss and black smoke will come out and sometimes stall. it doesn't do this all the time but is getting worse. it's a /94 chev 1/2 ton 4.3 with about 270,000 k.
any ideas?

Tune up time

Spark plugs, spark plug wires, cap, rotor, fuel filter, air filter, injector cleaner, clean the throttle body.

it was a mapping sensor.