What a huge difference it made to change my tranny fluid and filter in my 2004 X 4.0. The Haynes said change them every 30,000 but the owners manual says 60 or 65,000. It now has 76,000 miles on it and I thought it always did shift harshly. Now it shifts as smooth as butter and it seems quicker. It also seems to shift at more optimum speeds than it did before. This project has yielded instant results more so than any else so far. All it took was a 10mm, 13mm,and 18mm socket and a torx bit for the filter and that was all she wrote. Just thought I would share my results.