On a recent trip along I-40 across Arizona, I had cruise control set at about 75 mph, local maximum speed limit. A flat surface, tachometer showed 21k rpm (or so). Normally, I noticed that rmp shoots up to 25k or 31k or somewhere in between depending on road slope.
However, there were times when it shoots up to over 50k rpm out of blue for several seconds to maintain speed. Engine made loud reving noise for several seconds. I thought it ought to have accelerated somewhat gradually, not pumping acceleration just like that as if you press accelation pedal out of blue.
Western part of I-40 in Arizona have gentle slopes, albeit climbing if you come from California. Is this normal/expected behavior with cruise control?