I have a 2004 TL manual transmission.
Just had the original clutch replaced at 237,000 miles.
Before I replaced the clutch, the speedometer started behaving like the tachometer.
It's also doing it with the new clutch.
It goes up and down as I change gears. It also wobbles around the speed I am going.
I noticed it does it more when either the car is cold or it's cold outside.
Every once in a while it behaves normally.
Any suggestions as to what is going on?

 

VSS? have you checked this? any check engine lights?