Need help with tilt trim problem

[gsuggs]

I replaced electric motor and it will only move up and down a few inches. Motor stops running after moving outboard up a few inches. Sounds as if it binds up when it stops. Relays are working. Getting 13 volts at motor. When I disconnect hydraulic shaft from outboard it runs fine. It will go up and down all the way with no weight of the outboard and motor sounds ok ?? I have replaced the o-rings on the manual release valve with no change. PLEASE HELP !! Its the motor with square reservoir on bottom of motor w yellow plug

1989 MERCURY 40hp Classic
# CO202083