06 harley flhtcui, check engine light comes on when i hit 65mph, once I let off the throttle and get under 65mph it turns off. Any ideas?

The best way to check is to pull any error codes (DTCs) and see what the computer says is going on.

Turn the Ignition switch to the OFF position.
Set the Run/Stop switch to the Run position.
Push in the odometer reset button and hold.
Turn on the ignition switch and release the odometer reset button. The process has been completed correctly when the speedometer needle sweeps across the speedometer and all indicator lamps illuminate. The speedometer will also display "DIAG."
Press the odometer reset button once. "PSSPt" will display on the speedometer. Each letter signifies an area of the diagnostics testing, with the current selection flashing. Push the odometer reset button to scroll through the components for testing.
Press and hold the odometer reset button for 5 seconds, then release. Any codes stored will be displayed on the speedometer. If no codes are stored, the speedometer will display "NONE."
Press the odometer reset button again to view additional codes, if any.
Record the codes and refer to your service manual for possible faults or conditions.
Turn off the Ignition switch to exit the diagnostics testing.

Once you pull the codes, post them here and myself, or someone else, can look them up and tell you what they mean.