1986 Sea Ray w/170 Mercruiser/Alpha 1. Tilt goes down fine, but when trying to trim up pump motor runs but appears to be working very hard (slows down and gets hot) and the out drive will not go up. We replaced the up and down check valves in the pump, but that didn't help. We have reversed the the hoses out of the pump and it will trim up but not down. Today we discovered that if we disconect the down hose from the pump the drive will go up, while oil is being pushed out of the down hose. Thanks for any help.