1995 Chevy Blazer poor gas mileage and intermittent misfire

Blazer always had problem with going through O2 sensors. Replaced and soon after, engine light would come on and be reading O2 sensor codes. Cat is hollowed. Problems getting worse after water damage when water got in exhaust. Ran bad, stuttered, with black smoke. Changed plugs and o2 sensors, ran ok, then got worse. Changed fuel injectors with aftermarket, seemed to run ok for a while. Now rough at idle and low rpm, but not stuttering like before or blowing black smoke. When cruising on highway it will have intermittent backfire or quick stutter, and when letting off accelerator. Gas mileage is horrible, like 10mpg. Did I get a bad injector, think the o2 sensors are bad? The engine light is on reading o2 sensors.