'04 Auto Trans Shift Problem

'04 Malibu Maxx V-6 (with 52K Miles) with floor shifter and button shift on shifter handle. A few weeks ago the following started: When shifting from D overdrive to D, the transmission will downshift to
second on it's own when lifting throttle. When throttle is reapplied it shifts back to 3rd. If I press the shift button down once while in D, it does not downshift to 2nd as it should (yes, I'm going slow enough.) If I slow down more and move it down one more time it does not down shift to 1st gear as it should at low speeds. If I'm driving along in D overdrive and lift throttle and then reapply throttle (As is frequent in 40 mph traffic) the tach momentary goes up several hundred RPM and then settles back down where it was. It did not do this before at moderate throttle pressure.
The dealer says the car is showing no codes of any type.
Any ideas?
Jake
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The last condition you describe is normal TCC operation. When you lift, TCC disengages, when you get back on the gas, it reapplies after several seconds.

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