Pixelating and deinterlacing

I’m having a couple of issues with a first generation Fire TV hooked to an old Sceptre HDTV. The issues may be the TV an not the Fire box or Channels.

I was playing back a recording of Stephen Colbert Show which was recorded OTA. It pixelated as the stream loaded and when jumping over the commercials. But more annoying was the deinterlacing(?) or the horizontal zigzagging with any movement. The same recording plays fine on ATV and IOS.

Recordings from Silicondust Premium TV play fine in my limited experience.

Any suggestions are appreciated.

It’s a PIA to move the Fire box but I’ll do that when I have time and try it on a different TV.