Speedometer error, need help

[Errol C Johnson]

01 Sport Trac RWD, speedometer error actual speed 70mph gauge shows 61mph. Have replaced VSS, replaced instrument cluster, same problem, took it to the Ford Dealer they checked and can't correct or find the problem. Correct size tires and Ford said correct ECM parameters. using my GPS as my speedometer. Any help will be appreciated. Thanks

 

[410Fortune]

this is an odd one
Dakota digital makes a universal speedometer correction device for about $80 it should do the trick

Universal Speedometer Signal Interface

 

[Errol C Johnson]

this is an odd one
Dakota digital makes a universal speedometer correction device for about $80 it should do the trick

Universal Speedometer Signal Interface

Thanks for the advice will try that interface.