Maybe a senior member can help here. I have a 2006 S-type 2.7D with 120,000 miles on the clock. At about 50-60mph going up a long slight incline, the box appears to "hunt" between gears as shown by the revcounter and a faint regular 'burring' sound at a little less than 1-sec. intervals. Otherwise no 'lurching' at lower speeds as I've learned about here. Might this be a software effect, or could this be more serious? I understand this box is entirely under computer control.
Cheers for your advices, Leedsman.

 

That sounds like the torque converter lockup issue. Where the torque converter is locking and unlocking constantly.

Search, there's a lot about it, usually cleared by a reflash of the Trans control module.

George