^Thank you for the information.
I got this response from regional forum:
If the speed sensor is working and the speedometer registers speed when it is spun, then the drive gear inside the transmission (I'm assuming you have a manual trans) is stripped. That could IN NO WAY be caused by modifiying your car, unless your transmission has been disassembled. I'm not saying that is is common, *cough* yes it is *cough* but we have heard of it at Saab...
Oh, and the ECM has absolutely NO control over speedometer function on your car. (again, this only applies to a manual transmission car) There is a direct wire from the speed sensor that branches to the ECM, speedometer, and the cruise control module. If you took the ECM out and threw it away, and towed the car at 50mph with the key on, the speedometer will still read 50mph.
I have to take the car to another dealer. Hopefully, they fix it under warranty w/o any BS.