I've developed one...
Kinda.
It's a throttle-limited setup, which uses load on hills quite well. The design simply blocks the throttle that the cruise-control unit pulls.
The CC pulls the throttle cable similar to the foot pedal. I blocked the action of the rotating cam that pulls the cable -- basically governing the maximum throttle position. The TPS setting is around 20% maximum via CC.
Using it: set the cruise for 60 mph, for example. The car will generally hold the speed until the load overrides the throttle, then you scrub off speed and load it up. It works well if you're exhausted and have a long highway drive ahead. Then, the unintentional Psychology of not holding speed on hills is left up to the device and not your foot.
RH77
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