The 3rd gen 4Runners came with either an open differential, or with the optional E-locker.
With an E-locker, the diff was open until the button to engage the locker was pushed, then it became a spool, (no differentiation at all) until it was unlocked and was open once again.
If there is a button to the left of the steering column that says 'Rear Diff Lock', then it has the factory E-locker.