FT730v-efi runs 12-15 minutes , then starts missing

[slomo]

And the scanner is correct on the temperature probe, it’s not like an automotive sensor.

I hear you but how do you know? Have you used an IR or FLIR temp gun?

Try a USB bore scoping tool. Pull a spark plug out and insert this into the bore. See what you can see. Or pull a head off when you can. Good luck with it. Take pictures if you tear into it and post them here.