Q: Car revs up but does not drive faster than 40 mph on a flat road.

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I replaced the catalytic converter at about 150000 miles. Drove about 300 miles check engine light came on. Went to AutoZone scan said probably a bad upstream oxygen sensor. Replaced both sensors and light went out. Got gas one day and check engine light came on again. AutoZone said it was probably the gas cap. Replaced cap and reset light. The other day I pulled out and car died. Got it started back but it won't do over 40 on a flat road. Engine will rev but the car slows down. Any idea what might be wrong? The check engine light is not on so I am puzzled. Thank you.

My car has 163000 miles.
My car has an automatic transmission.

Hi there. For the engine revving up and the vehicle slowing down, the transmission could be slipping. Check the transmission fluid and see if its full and red in color. If the fluid is full, then the transmission could be slipping while in gear. I recommend seeking out a professional, such as one from Your Mechanic, to help you diagnose your transmission.

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