Before I do too much taking apart things, I'd get under it and check the lift mechanism. I believe it is a Goshen mechanism if memory serves. You can check the pulley and cables. While you are under there, use a grease gun to grease the zerk fittings. If it hasn't been serviced, it may take a lot of grease.
If it still doesn't lift, take the cover off of the power lift and check to see if the gears are well greased. You should also be able to see how to manually raise the roof. If it still binds up when manually raising the roof, I would guess you have an issue with the wiffle tree in the lift system under the Pup. If it raises fine manually, only then would I look at the motor as the issue.