Yes, I have done my tranny twice now. You could take it to a trans shop and save yourself some labor and mess, but spend the money, or you can just do it yourself. Its kind of a pain in the boot, but it isn't that hard as long as you have the space, time and a helper. If you want more specifics, PM me and I will break it all down for you. Otherwise, yeah, at that mileage, I would say your tranny is suffering if you have never done a fluid/filter change.
Bart