That is about the same speed as the torque converter lockup. I suggest that the lockup disengages when you apply gas and because of the light throttle application, locks up again. If this is the case, nothing to worry about.

The TCU/ECU are 'learned' modules. Because the driving habits of the PO and your wife are different, it might just be 'relearning' and settle down after a while.

Unrelated: Most dealers use regular oil, switch to synthetic to keep the gunk buildup to a minimum. If a dealer says they use synthetic, ask to see the drums of oil.
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Keeping it running is better than buying new