Here's a link to a TSB that everyone raves about on the tundrasolutions forum:
I will be performing this fix in the next week or so on our 2002 when I also replace a lock actuator on the liftgate (found some sources online at about $30 less than dealer price).
If you do find you need a motor, there are places online that sell remanufactured motors for $60 or less, but they are specific to the liftgate, though others have reported a similar year 4Runner motor also works.
I have found that the dealer personnel want to replace rather than do a repair -- less headaches for them and more profit.
A little research for the consumer pays off.