2016 Sealed Transmission Problem

2016 Rav4, gasoline base model with AWD and automatic 6-speed sealed transmission. 298k miles.

Operated normally at highway speed (70mph) until a stop at a rest area. Car was not shut off or put in park for the roughly 3 minute stop.

While accelerating back to freeway speed, the transmission seemed to "miss its shift" from 4th to 5th gear, allowing the engine to free rev. After a 2-3 second count, the transmission "caught" and accelerated normally to the 5th to 6th gear change, where it again missed the shift, free revved, and caught again after 2-3 seconds.

At top gear cruise, even at much lower speeds (40mph?), there is a transmission "pulse" or a felt "power surge", accompanied by a fluctuating rpm, as indicated by the tachometer.

I assumed a low fluid situation. Transmission was brought to recommended operating temp (104-113 degrees) and pan drain plug removed. 30 ounces of a very dirty, not quite black, trans fluid came out. Overflow tube (it's green) appeared to be in place within the pan drain hole. A little over 30 (31?) ounces of new fluid was added.

Test drive afterwards yields same condition, except that the "surge/pulse" isn't as hard.

Questions:
When brought up to operating temp and engine off, and the transmission filled to its proper level, should there be any fluid that comes out of the overflow tube?

If I were to do a full transmission flush and fill, dropping the pan, how much trans fluid does the system hold?

Can the condition be fixed easily? Is it over full? (Car was supposedly fleet maintained. Although the condition of the fluid indicates that it wasn't changed.) Can reducing the amount of fluid, until it doesn't run out of the overflow tube, help the situation? Or will it hurt?

Worst case scenario, how much does will a replacement transmission run me, for parts and labor?

Have you experienced anything like this?