Ben.

We have an intermittent Jake Brake probem, too. The check engine light will no longer come on. The Jake indicator activation light stops working and we can feel the Jakes have cut out.
Have you tried shutting the motor down and then restarting it? At first, we thought it to be a loose wire on the DDEC. Try to trouble shoot it with S and S, we determined if we shut down the engine, let it sit for a few minutes, start it back up, all resets and we have Jake again. Our September trip of 3,500 miles, the Jake only cut out when we were in stop and go traffic in Vancouver, BC. Other times, it has cut out off of Loveland Pass, Yeeow!! Know what you mean. I don't care at the speed. When the Jake cuts out, we go down a hill either in the gear we climbed or a lower one so we don't have to punch to service brakes so much. I just stab them, and slow the coach down as Jon described above. This way, the brakes stay cooler, and you don't run out of air.