I have a 2000 40hp Johnson. The tilt would pick the motor up but as soon as I let off the switch the motor would slowly go back down. It I was driving the boat id almost have to hold the switch just to stay trimmed out and on plane. I took the boat to a guy my dad knew who said he could fix it. Thankfully he didn't charge me anything and said the whole unit has to be replaced and all he really did was change the fluid. I had already made sure it was full of fluid and knew that wasn't the problem. Now it doesn't try to lift the motor at all. I've even had someone pull up on the lower unit while I held the switch. The motor is up and locked but I can't raise it to unlock it. Can the tilt unit be rebuilt on these models? What can I do to be able to get the motor to raise up?

I'm sure it can be rebuilt. Parts should still be available. There is a manual release valve that you can unscrew a couple of turns and that should release the pressure so you can raise it up.

Mine was just a relay replacement.

http://www.boats.net/parts/search/BRP/JOHNSON/2000/J40TPLSSM/POWER%20TRIM%20%26%20TILT/parts.html