I can confirm that the TCL 55R635 tops out at 4K-60Hz. If I set a game to run at 4K-120Hz, which is what I did for Resident Evil 5 on my PC, the TV will accept the signal but it will downgrade it to 60Hz. So, if it's any consolation, the TV can at least accept a 4K-120Hz signal, but it will not display the signal at 120Hz but will display it at 60Hz. Also, I tried Resident Evil 5 at 1440p-120Hz and it worked; the TV both accepted the signal and displayed the game at 120Hz (I confirmed this by pressing the "OK" button on the TV's remote, which prompted the TV to display a tab that listed the resolution, refresh rate, and the audio type). I didn't try this with a game that can be displayed in HDR, because I don't think that my computer can run any such game that I have at 1440p-120Hz (e.g. Mass Effect: Andromeda), though I guess that I should have tried (I'll try tomorrow, but I have to go to bed now).