Sound problem on 4k tv at 1080i h24 receiver

Just got a new tcl tv and am having problems with the sound.  The receiver is defaulting to a 1080i signal.  There is no audio with the Dolby turned off on the receiver.  If the Dolby is on, it blurts little segments of audio.

If I manually change the resolution down to 720, audio is fine.

I tried using the res button on the front of the receiver, but it won’t output in 1080p.

I have tried both a generic hdmi cables, and one that is labeled “sapphire high speed with Ethernet.”  I have tried all the menu settings for audio on both the receiver and tv.

Any ideas?  Ideally, I would get the sound to work at 1080, but I would also be happy if could get the 720p as a default out of the receiver.

Thanks for your help!