I could not resolve this in the FAQ or else ware...

I have to 1080P webcames, A Microsoft Lifecam and a Logitech c615.
Using either, I can record 1080p 29.xfps perfectly fine either with
the lifecame software, the logitech software, or Wondershare Filmora
but I am trying the 60 day trial of vMix and love it except it cant
record smooth video for 1080p or even 720p on either camera.
Preview is fine, but start records and its laggy. Its not just the
preview while recording but also the end result file.
I am connected to USB 3 ports, computer speed is fine since records fine
with other software. Have tried 1080, 720, every recording format
but nothing working.
Also tried saving to the internal SSD instead of the external storage but
its always bad.
I think I have tried everything i can find, been playing with it all day long.
Both cameras do the same thing.

Any ideas?