[BLSTIC]

No add-on *electronic* module will work correctly with modern software, unless you made a module that intercepted the throttle pedal signal.

Most throttle pedals have two potentiometers in them, that are opposite in effect (one goes, say, 0-5v with increasing load, the other goes 5-0v with increasing load). As long as both signals add up to 5v the signal is valid and the pedal is deemed not faulty.

To fool this in the least intrustive way you would need to know the required throttle to maintain the speed, and use something like an arduino to switch in both fake pedal signals while over speed and over this throttle position. This would close the throttle *to the correct amount to maintain speed* (as opposed to completely) when at and over speed, while still allowing torque to be controlled to lower levels. It would, however, have a fault if for some reason, like a headwind/tailwind/trailer/hill in that it would still allow overspeed if the power requirement was lower or pulse around the limiter if it was higher.

Your best bet is to access the factory PCM and change the limiter settings, as nowadays they automatically close the throttle if you approach the limit slowly and the transition to 'limited' would be smooth and accurate. If you do this, the chances are that you then have access to auto trans tuning too, which is a powerful economy tool