1995 Jeep Wrangler Chugs and misses and backfires

Check engine light came on and coded 02 sensor. Changed sensor and still coded same and would run good for 10 miles then chug, sputter and backfire when under load until rpm's were high then would run ok until under load again at low rpm. Changed fuel filter and cleaned throttle body and ran real good for about 20 miles then went back to running bad but check engine light does not come on. Had recently added fuel injector cleaner and ran about 30 gal of fuel through system. Fuel that ran out of filter when changed was black. Have new plugs to put in and have not sprayed water on plugs, wires and cap and coil to see if ant sparking.