Descending gentle hill under cruise control?

Using cruise control set at ~40mph there’s a gentle rural hill that my TLX-V6-Tech regularly travels (car in “Normal”). It ascends the hill with very little loss of speed or change in tachometer. However, descending is a tad troubling: the car slowly accelerates (expected) — and suddenly the tachometer surges along with a sudden increase in speed! Of course, I gently apply brakes to bring the TLX back to normal! My previous 2010 TL would never have acted this way…

Anyone else have a similar experience? Is this a problem that can be corrected?