Tbf to the Hisense U8k the 720p upscale is pretty decent, but as mentioned I may order a Shield Pro from Amazon to test against it to see if the upscaling is worth the value vs TV (as we already know it beats firestick).This is how I use my device and app settings so that the TV knows the native resolution, frame rate and refresher rate.
The black screen is the device and app switching the settings and is normal.
Not sure what settings you should use for a Hisense TVs as I have never owned one.
Also I would imagine 720p image upscaled is not going to look that great on a 75 inch TV but that will also be down to how good the TVs upscaling capabilities are and this varies from each manufacturers on low, mid and high end TVs.
You will have to find specific reviews for your TV and their views on how good the upscaling is on it.
Yeah after testing this is the resolution changing between each channel (720/1080/2160).When I have Match Frame Rate set on my 4k max Firestick it goes black for few secs on my Samsung tv as well
The only anomaly I noticed was I put a SD channel on but Hisense detected this as 3480x2160 but I wont use many SD so not complaining lol.
And lets hypothetically say the Shield Pro is better than TV for upscaling. That means I disable the Tivimate settings (Screen Resolution Match & Refresh Rate) so that the Shield can take the 720p and upscale it itself rather than the TV?