[FoxForceFive]

I use just my TV speakers so should I whitelist all resolutions including 1080p ones and it works smoothly even for 23.9 files on RC5?.

I currently am using RC4. Is there much difference in RC5?

I don't have anything whitelisted.

What seems to have helped is setting display settings to RGB and 10 bits in firestick settings.

 If you're just using your TV speakers then the obvious answer would be to leave the refresh rate alone completely & just have sync playback to display enabled as it will resample the audio, should play all content smoothly that way.