1996 Chevy Caprice car hesitates bucks under light throttle

Engine Performance problem
1996 Chevy Caprice V8 Two Wheel Drive Automatic 255k miles

i have a 1996 chevy caprice with a LT1 350. It is idling rough and hesitates or bucks under light throttle but it will still get up and go and smoothes out at faster speeds. It also idles extremely low (500 600 rpms) and revs too high at highway speeds but never stalls its very intermittent but seems to get worse as engine warms up it has true dual exhaust so I can tell its sputtering or missing on driver side only. Ive changed plugs n wires fuel filter checked vacuum lines and EGR valve these are all good. My opti spark distributor may be bad it had oil dripping on it but im not sure its too expensive and hard to get to its underneath H2o pump behind balancer pulley. Car has NO trouble codes except O2 sensor which has been bad 6 yrs with no driveability issues car does not smoke or use any oil either. Could distributor be my problem or does it sound like something else(clogged cat, valve problem etc)?