bronco runs rough

I have a 1993 ford bronco 5.8(351)..when the engine is cool and warm it runs really rough, the rmp gauge jumps around, the vehicle shakes and when I try to accelerate it spudders real bad. Now this happens the majority of the time but not all the time, sometimes I will start it and it runs great the whole day. I replaced the o2 sensor located underneath in the exhaust and the fuel filter. The coolant temp sensor is fairly new but the plugs, wires and rotor are fairly old. I cant hear anything like a vacuum leak under the hood...any ideas?