Dad has a 2004 LeSabre, your typical 4T 65E and a Series II 3.8. Beautiful car runs great and shifts great about 120 K on the clock. After you've been driving the car for a while, out of nowhere the car will start to shift very hard almost as if it is commanding full line pressure. When this happens in the shifts will actually make the tires chirp sometimes. If you throw the car in neutral turn the key off and restart the engine it'll drive and shift fine for another half hour or hour. I think I've vaguely remember seeing about this and the fix was some sort of Mr. shift kit or maybe a couple of new springs in parts of the valve body or there is a cover you removing in the trans and a couple of new springs go in. Years ago I remember reading something about the transmission computer detects a ever so slightly longer shift than what it calls for so it thinks there's an issue and goes into a limp mode and commands full line pressure. Maybe some of you experienced GM techs or other folks know exactly what this is? I don't think the trans is failing though because until this happens the thing shifts beautifully and gives no indication whatsoever of any issues. Fluid and filter has already been changed and the trans has been maintained very well.