shortly after i bought my 01 last year, it would occassionly not shift up into OD. it seemed to only do it on real hot days. so going down the road at 55 i would push OD on/off and nothing would happen. i changed trans fliud a couple of times, about a month apart, and it quit doing it. Old fluid was really nasty and had a lot of sludge on the magnet. welcome to df and good luck.
http://www.pavementsucks.com/tech/trans.php (don't adjust the bands unless you have a slipping problem)