I came down a 6 mile long 6% grade yesterday, To come down that long foe that steep a grade without using the service brakes I had to come down at 39 miles and hour and in 3rd gear. If I went up to 40 MPH my coach would shift into 4th gear and I would have to stab the service brakes to get back under 40. Just start down slow enough and you should not have to use the service brakes at all if everything is working as it should be. Just have to "learn" your coach. With that said there are times I would sure like to have a Jake brake rather than just and exhaust brake.