Recently traveled from NW Ohio to the Black Hills and then onto Yellowstone. I have an 07 Itasca w/8.1 Vortex and the 6 speed Allison. I was towing my 3300# PT cruiser on a dolly. I noticed while in the high alltitudes, steep grades and long pulls, my transmission seemed to howl. It was very noisy in the cab area. It was not the cooling fan as I have heard that before in this unit and my previous coach.

The excessive noise disapated when we got to lower altitudes and flatter roads ie: Illinois, Indiana and Ohio.

Any help would be appreciated. This is a new unit with about 4500 miles on it.

Talked to my dealer today - he said it is the grade brake. First time he took one across the mountains to California he thought the coach was going to blow up!!

Problem solved.

Did that dealer explain the relationship between the grade brake and you climbing "long pulls"? The grade brake feature is designed to help slow the vehicle on down-grades, and should not be activated when receiving torque from the engine.
I would feel much better asking Allison directly.

As I understand it, the grade brake is activated by tapping the brakes, which forces a downshift for a compression assist, but only while crawling downhill, never up, right? When I've used mine, it seems to downshift EACH time I hit the brakes until the engine is revving too high (screaming,I think), so I just switch it off. Am I doing something wrong?