It must be the presurre releave valve. I'm not sure but I think u activate that when u step on the inching valve. Anyway you can shime up the pressure releave valve but u have to hook up a pessure gauge to chech it. Factory setting was about 6900 psi for a 2388, I've gone up to 7400 without trouble. Helps alot when u have rear wheel assist and run in a lot of mud.