After starting off on a long road trip last week (isn't it always the case?), I noticed my XKR wasn't shifting into 6th. It previously did this around 48pmh in regular mode. Even on the freeway, it stayed resolutely in 5th until I floored it to get round a truck, and 6th finally kicked in at 80pmh. It stayed in 6th at lower speeds until it downshifted under braking or hard acceleration, when it went back into 5th and stayed there until the next time I hit 80. Even at 80, it will drop back into 5th if I select sport mode. One week on, the problem hasn't gone away.
I've already been having the "Check rear lights / Cruise not available" warning for a few months, that's been covered in other forums, but this seems unrelated. There were a whole bunch of electric issues a couple of years back - the usual suspects - all of which were resolved when I replaced the battery.
Any ideas?