To help you make a more informed decision on this high ticket item, why not take it to a dealer and have them do a complete transmission flush including drop the pan. It won't be cheap ... $300+ but they should be able to tell with a visual inspection and a review of the "droppings" if any in the pan, if any, overall condition, trappings in the filter (felt/screen?), etc. Should you decide to keep it, the full tranny flush and clean should extend the life of the transmission.
Should you decide to get rid of it, the 2014 Highlander is awesome.