I have been driving one for a week now. I can tell you that the rumors about the "Jake" are false. The trucks do have Jake brakes, however, as of now, the driver has no control over it's operation. Here is how it works...............
With the cruise control on,,,,,,,the C.W.S. moniters the lane in front of you for other vehicles.....when a vehicle is in front of you and is going slower than you are, first you get a visual warning....giving you distance and speed of the object.......if the distance between you continues to decline, about 300 ft out, the truck will automatically start to back off the throttle to adjust your speed to his.......if this doesnt' work fast enough, and the distance is still decreasing, the Jake will come on to further slow you down to match speeds with the lead vehicle......IF this still doesn't created the distance needed, the truck will automatically apply the brakes in a tapping motion to further seperate you from him.
So...........you have a long hill to go down........keep your Cruise set, get in behind another truck that is doing about the right speed down the hill, and follow him. When you get too close, the Jake will come on and stay on as long as you don't touch the foot brake..........if the jake isn't holding back enough, and you get too close, the TRUCK will apply the brakes by itself, to back off the leader far enough so that safe distance is maintained.....Since the truck is applying the brakes, not you, the crusie control stays on and the jake works all the way to the bottom.