have you checked your trans fluid?
got any dents in the trans pan?
Been off roading?
Does it make a squealing sound sometimes? A lot?
^^all trans issues^^
Check the pinch welds on the rockers. If you've been thru a lot of water and the pinch weld openings get cruddy with debris like mud or under coating or sand the water never drains out. A simple cram and twist with a beefy screwdriver opens them up enough to allow drainage. Its common on early Bajas due to over application of under coating, but others due it to mainly from clogging up from offroading.