Our 2016 XJL - 40K mile transmission is reluctant to shift to a higher gear when in "S" drive. This also happens when I use Dynamic diving in either "D" or "S". All is fine if I just use "D" drive. It will upshift through the first couple of gears then stop upshifting, leaving the engine running at 3,000 to 4,000 RPM's. Sometimes, if I hold a steady speed, it will upshift a gear or maybe two, but never lands where it should. If I engage Cruise Control, the transmission will upshift properly and operate normally.

Since it performs properly in "D" drive and also on Cruise Control, I'm thinking it's not so much a mechanical issue as maybe it's a software issue? Has anyone experienced this on their XJ? Any clues?