2019 TRD Pro downshifting over 80 on cruise control

As the title suggests, I'd like to know if anyone else has had the same issues. The truck is around 200k miles. I was driving with the cruise control on for at least 4 hours, speeds around 75-80ish mph, and randomly, the RPM's fire up, and the truck downshifts. It's happened twice on the freeway so far, and there are no codes. I pull over, shut off the truck, and it starts right back up. I've brought it in to Toyota and just had the spark plugs changed, and they did an oil flush with "seafoam"?? I am not a mechanic, so unfortunately, I feel like I got taken advantage of, because on the drive home, it did the same thing. I just want to fish around this page before I bring it back in. When I'm not using cruise control, it drives fine, no issues. Any suggestions are appreciated!