1996blazer runs good, get up to 30-35 hesitates until let off gas and press again, when it hesitates black smoke and sputtering

If the above answers don't work for you, the cat converter could be blocking up.

First change the Air filter, Then perform an OBDII scan of the stored fault history. Look for a (MAF) mass airflow sensor or (MAP) manifold absolute pressure sensor. The only sensor that is subject to physical wear(1996, age) is the (TPS) throttle position sensor. Let the OBDII scan be your guide to any repairs to avoid buying parts you don't need. A dirty air filter can put the mass airflow sensor out of range. Do the cheapest fixes first.

It sounds like you might have a misfire that is causing the engine to run rich, hence the sputtering and black smoke. When is the last time that you replaced the spark plug wires and the spark plugs? If the 1996 plug wires are like the 1997 plug wires used on the 4.3L S-10, they can be pretty difficult to get a reliable connection at the distributor cap.