02 Grand Prix frequent shifting into OD

Greetings ETCG members,

As of last week my GP developed this weird shifting into OD too often. It’s motorvated by the 3.8 N/A with 76K miles

For example, going to my Mom and Dad’s place, in order to get there, I have a to climb a slight incline to their driveway. I could be going about 20mph and the car would shift into OD and lug the engine. I have to put my foot about halfway into it to get it to downshift.

Even just going around town, it seems it shifts into OD for every little thing. That said, it doesn’t skip any gears, shift hard nor delay. It doesn’t feel like it’s slipping neither so says the little tachometer nor my butt dyno.

For the fun of it, I changed the tranny oil for the first time ever since the car was new. Prior to this, the fluid draining out was nice and red, smelled normal and full to capacity. While this was going on, I had the battery unplugged(cold engine) There aren’t any codes but I figure it can’t hurt anything. I did not add any additives as I don’t believe in them, but perhaps I could be convinced? Test drove and it still doing the same thing.

I apologize this is long winded but I figure I should give all the details. What do you all think is going on?

For the record, the car is totally stock and has been since day one. It has never been raced, molested nor abused. It’s an 11 year old daily driver. Also, I don’t want grief for the fluid not being maintained beforehand. I’ve had the car for a year and the previous owners did not change the fluid.