My 5.0 S/C has developed a few problems which I believe to be gearbox related.

The first is an intermittent juddering when driving around 1200rpm-1800rpm. This doesn't happen all the time, it's usually when the car is hot. Switching to sports mode to make it drop down a gear/increase RPM stops the juddering. During the juddering the RPM surges up and down around 100rpm-ish. This sounds like a torque converter lock up clutch problem as in some of the earlier boxes. I've not seen any reports of it happening on the 6HP28.

The second issue is an occasional hard shift. This happens when transitioning from coasting to being back on the throttle (e.g. coasting towards a roundabout and then getting back on the throttle to go). I'm a little unsure about this one as it feels as if the engine is disconnected from the rest of the drive train for a second and then it bangs back into gear. Again I'm wondering if this is something like the lock up clutch getting applied too hard.

These issues don't present themselves every drive, only occasionally which makes gathering data from them hard. I've changed the gearbox filter and fluid but that didn't yield much improvement. The old oil didn't look too bad. I'm going to try gather some logs with my IIDtool when I can next replicate it.

Do any gearbox gurus have any thoughts or have any other 5.0 S/C owners had anything similar?