Ok I replaced the Speedo gears on the inside of the transmission and the one on the cable leading to the speedometer. Now my speedometer runs backwards. Any thoughts?

 

Just fyi the gears can only go on one way. And C
According to ford they are the correct gears for the 3.55 rear end

 

Run the miles down.. sell it. Has to be either the wrong gear or wrong installation.

 

Probably the wrong speedo adapter. Take a pic of it.

 

Sean is right. The gear runs opposite on the new one compared to the old. Now I have to start looking up part #s again to see if I can find the right one. Ford told me they don't stock anything but the most basic parts for my truck.

 

Junkyard. One from most any F150 transmission will work.

 

Another method would be to google ford speedometer gear.