Did you examine the inside of the gear to be sure the cable fit tight? I'm sure you did but just tossing it out there. I have never seen one fail there, usually it's gears but you never know. It sounds like if the gears are good and the speedo turns it's the cable, so what can change about the cable making a working cable not work? I am thinking where it goes into the gear is all you have left to look at.