I would check your wiring first. I believe that most mechanical lifts are powered by wiring that runs from the battery all the way to the dash switch, and then back to the hatch lift. If the wiring is too long, or if the switch is not 100%, you will have a large voltage drop. Try running the lift once manually with short heavy jumpers directly to the battery. This will let you know if the lift is O.K. I have also seen where the sunpad is so waterlogged that is makes the hatch assembly too heavy for the lift.