I bought a used 2001 Corolla with 84K miles. The transmission shifts too early at 15 mph and 30 mph. I don't have an overdrive button so I believe it's a 3 speed.
Shifts are not rough and there's no clunking or slipping. The fluid looks cherry red.
I have an exhaust leak before the cat and so I have an O2 sensor code, but no other OBD codes.
Would an O2 error cause that or if not, what should I look at? I'm concerned that running the car at highway speeds is red lining the engine. I can't tell how badly since I don't have a tachometer but it sounds like it's racing even at 50 mph