I know there has been some issues with the 4k or uhd with the Amazon app(2 days ago it didn't even list uhd). But I see UHD on the Grand Tour but when I play it I only get HD 1080p and I don't see an option to upscale it beyond that. Anyone else have this issue or know the solution?
Had the same problem, make sure you turn in uhd color in the settings for the hdmi port of your TV. Once I did that I got 4k amazon prime