It does sound like a pressure problem. Your motor for the top should have a resovoir attached to the pump or the motor it self. Check for a filler hole to put fluid into that assembly. The fluid level will vary from what ever position the pistons in either extended or retracted. You would not add fluid to the cylinder it self. Check for level of fluid both in the extended and retracted state. Too little fluid will not give you full extension and too much fluid will blow the seals.