I am thinking three possible scenarios:
1) your lift mechanism has become corroded over time and it more difficult to operate. Find the manual override on your power lift winch (usually a plastic cover with a hex bolt underneath, and a handle to manually crank) and try cranking. It should crank easily and smoothly, if rather slowly. If not - then this is probably your problem.
2) the power winch motor is going bad and heating up. IIRC these actually have two built in limiters, a physical limiter set on the cable that once the winch reaches that point it shuts off and heat or current based breaker that shuts the winch down when it gets too warm. IT is obviously not the first one, but if the winch motor is going bad it will get hot quick.
3) the switch itself is going bad and giving you intermittent contact.
2013 Coachmen Freedom Express 320BHDS pulled by a 2005 F250 King Ranch CC
A rainy day camping is better than a sunny day at work.