Isolate the ground of your laptop. As mentioned .
How much different? Higher ? Lower? Is it a stable readout for both?
Are you using Smart Voltage or are you writing in your own nominal Voltage?
I write in a Nominal Voltage for anything 14ga or less.
Why kind of Plasma Cutter do you have setup?
Whats fast ? My go to for 14ga mild steel on my crossfire pro is 270 ipm. (book Hypertherm cut charts)
How are you observing this slowness?
At 200ipm plus I couldn’t visually tell what micro adjusts the z axis is making.
I find the readout in firecontrol had quite a bit of lag also. even the visualizer and G code read out runs behind the actual cut.
Are you getting cut quality issues? Is that why the focus on the THC?
Make me wonder though.
What is the feed rate of the z axis when being control by the THC?
How much latency is there in the VIM circuit?
Is there a different in latency between raw or divide voltage through the VIM?