My transmission doesn't want to shift out of low gear, what do I do?

I recently added the wrong type of fluid (dexron) and drove it around for a couple of weeks. It still drove ok, though it wasn't quite right. It finally hit me that I added the wrong type of fluid, so I removed the pan and replaced the filter and added the correct fluid (ATF+4). Now when I shift it into gear it isn't very smooth and it wont shift out of low gear.