I tried that and it shut off in 15 minutes .
Another driver showed me a way with the cruise control button, the words "engine throttle" illuminate on the speedometer. I tried it and it worked but a few minutes later down the road it didn't work. I will play with it throughout the day.
Yes some are designed to shut off once the truck motor idles at below a certain amount of revs the idea is you'll need to keep the revs up to a higher level I'd usually adjust mine to about 1100 rpm as running an engine to long at low revs is not good for the motor.