Have a similar issue on a 2001. It shifts fine when I start it up, and shift to 1-2-3-4-5. However, sometimes it will not shift back down. It sounds like it is trying though, and it actually "clicks" each time I hit the shifter. It is worse when the engine is cold. If I stop the engine, and then just turn the ignition on without starting it, I am actually able to shift down to neutral. I wonder if the battery is getting bad somehow. It has been a long while since a battery change. Thoughts?