On your hoist--there should be another knob, or lever that goes to another valve. Check to see if that's fully engaging. Maybe it's hung up or sticking.
I know this goes without saying, but if you do get it lifted up--manually or otherwise-- DON"T go under there, unless it's supported VERY securely!! Even then, I would avoid it if at all possible. Do as much as you can from underneath the truck. I knew a guy once who got killed when a truck box fell on him.
