Not a CPU issue on my mac, at least, but that did lead me in an interesting direction.
So I was double checking and saw the usual EyeTV process at ~10 to 20% cpu back and forth, but also an EyeTV H264 Decoder process also with about the same.
Which is weird because this should be MPEG-2, not H264.. Upon loading the HDHomerun's web UI, it was offering transcoded streams which I absolutely don't need.
So needless to say, I disabled that and went back to just native MPEG2 and it's ..... better, but not fixed. Still stuttering. So I'll keep looking in the HDHomerun angle, not EyeTV, for now. Thanks!