I have a 2012 Kenworth T660 with the ISX Cummins. I am having trouble with the 3 position engine brake not working all the time. This problem has been going on for a while now but it’s really starting to bother me. Most of the time I have to downshift before it will work. Other days, like yesterday, it worked flawlessly. As soon as I took my foot off the throttle it started working. Today, it worked two times at the very start and one time at the very end after I down shifted twice. I notice too, if I switch between the three positions of the brake, it will quit working for an extended period of time. I bet tomorrow when I fire it up, it will work just fine, and then not the next day. Before I take it to the shop and pay $175/hour for them to throw parts at it, is there anything I should look at first? Appreciate any input.