Had engine work done in April. Ran fine after. Was out of the country for 3 months and car sat in front of the house. Trans fluid was low when I got back. Car runs well, but transmission now shifts very rough 3rd to 2nd, and especially 2nd to 1st... with a loud "THUNK." Changed fluid and filter, and fixed slow leak. Fluid level is now fine. Problem of rough shifts persists unchanged. No idea what I am dealing with.