I have an 07 STX special edition with a 5.4 3V (#2) engine and a 373 rear end.
About 2 weeks ago I noticed my speedometer didn't match one of those speed check devices on the side of the road. By using the WAZE app and MAPS app I realized my speedometer keeps correct MPH up to around 40MPH then it jumps up 12MPH over what its saying. I've heard multiple possible solutions. My question is this is there a pattern or more likely than the.other solution that seams to be it. Really dont have the $ to do a process of elimination.

 

Was one of the solutions you heard to replace the cluster ?

 

Yes and the other was the sensor on the side of the transmission and I've heard needle may be stuck but it does it at 40mph everytime and it stays at 12mph over what it shows so unless it sticks and accelerates at the same rate everytime I'm guessing that's not it.