I recently obtained a 2000 Cherokee with 99000 miles. I do not know the history, but I changed the coolant because it was black with thick sludge in the overflow container. With this in mind, I wonder if the transmission was serviced? I have heard if an automatic transmission has never been serviced, it is better to leave it alone. Something about screwing up the bands and pumps. My knowledge of transmissions is when you put it in gear it is supposed to go. Currently it seems to be working fine, but what do I know, I'm used to straight drive. Any guidance is greatly appreciated.