Transmission 4th gear to 5th gear

Link to the video down below

So I'm having a weird issue with my rpms when shifting from 4th to 5th gear. I have a 06 taco with 86000 miles, it's a 4l v6 with a 5 speed auto transmission.

So if you see the video it goes into 5th gear around 41-42 mph. So when it's doing the gear change my rpms goes from 1800, to 1500rpms , then drops one more time to 1300 rpms . I'm not letting my foot off the gas pedal. If you you look at the mph gauge, when it's doing the shift from 4th to 5th I'm gassing the whole time. And if listen closely you'll hear it when the rpms drop twice . I've done a transmission flush about 3 months ago hoping that's what it needed but it's there.


https://youtu.be/qVZsYqwTvwg