My Cummins/Allison DP has a Jake Brake, which works A-OK. It also has cruise control which works A-OK.

But they do not work together! If both are engaged the tranny constantly down/up/down shifts.

The Jake and the Cruise seem to be at war with each other.

Comments & Suggestions?

Sounds like they are working correctly to me... as soon as torque is released, the Jake starts to work, backing up exhaust gasses putting back pressure on the cylinders, hence, using the engine to brake . The cruise is constantly appying and releasing throttle... as it's supposed to to maintain speed... and when it releases throttle pressure, that is causing the Jake to think it needs to cut on to apply some braking. Then, the rig has slowed, so the cruise tromps on the throttle to get back up to speed, etc. etc. etc. There is no real need for the Jake unless going down long grades, when you want to save your brakes from overheating, so I'd manually control the Jake for those times it's needed. "If it ain't broke..."