1997 3.8 Camaro with Auto tranny. As the title says, speedo is off by 15 mph. Reads 70 when I'm doing 55 .confirmed by multiple Phones GPS apps, as well as the general flow if traffic :/. Bought the car this way about 2 months ago. Drives me nuts!

 

wondering if someone put some different gears in the rear. you can have the pcm reprogramed to adjust the speedo for different tires and gears.

 

I was wondering that kinda.. but it doesn't feel spunkier than the 3.08 that the option codes say I have. Plus would that make a 15 mph difference? I was thinking a rear gear change would do like a 10 moh difference, MAX. But I don't know because I've never done it!

 

You didn't mention the transmission was shifting funny, I wonder if its a gage matches the PCM info.

 

Doesn't shift funny, just reads incorrect. Is there a way I could see what the pcm is outputting?

 

Yea, any scan tool or you can get one of those blue tooth OBD2 adapters and a app on your phone.