Put the end point adjust on the transmitter back to 100% and redo the setup routine on the speedo.
Check the transmitter and make sure you haven't got expo or ather settings all over the place.
One thing that gets me every time on Spektrum Transmitters is the insane amount of throttle travel the transmitter has. Coming from Sanwa or other transmitters I never pull full travel. Make sure it' not this silly mistake... I made it with a friends DX3S and felt a right tit after complaining about the car being slow
