What's wrong with my speedo???
 

Have a '97 firebird formula, A4, 2.73 gears and the speedometer runs slow. It seems fine when you're going 20-30 mph but it slows noticeably when going faster than 40-45mph. I've checked my gears using the chalkline/driveshaft method and it checks out at 2.73. My tire size is also correct. Everything matches the door plate. So is this a speed sensor problem? All other gauges are working normally. I do have the SES light on but according to autozone, it scans as an O2 sensor being bad. So what is the problem here?


BTW- the car runs fine and the trans shifts normally as well.