Q&A

I recently bought a 2000 Nissan pathfinder. The service engine soon light came on as I was driving. The codes ran as a knock sensor and oxygen sensor in bank 1 and bank 2, high voltage. I notice around 35 mph the engine or transmission shudders. The car sat on the lot for a couple of months, so my first reaction was old gas. I filled it up with plus after running all of the old gas out and adding sea foam. Does this sound like a transmission problem or could a knock sensor be causing the shudder? The car switches between gears at low speeds without problems, including taking off.