97 3000gt sputtering at half-throttle?

One major thing is i need to change my oil BAD but i don't think that it's related to the sputtering. I was thinking it's electrical so i disconnected my chip and it's still bad. I'm thinking maybe a bad O2 sensor or a clogged cat. It started happening very suddenly and randomly. Although i did run her pretty hard the night before. Maybe even a spark plug going out cause i've got oil leaking from my cap. I don't know, It only happens when i push it past half-throttle, it doesn't react to the rpm's. when it sputters, the tach stops and moves accordingly between sputters. It's rather frustrating and I would appreciate some input.