Jeff,
The THC slider sensitivity was fixed in a recent profile update. If you don't want torch height control you can turn off THC mode and use the M3/M5 scripts to turn on/off the plasma. It should also be possible to map the THC up/down to some inputs that will not receive any data. In other words, don't connect them to the THC, then the torch height motion won't happen while in THC mode. This will not work though if your material is uneven and it has to move up/down. The Proma THC150 works directly with the HiCON Integra controller to control the up/down motion of the Z axis height while in THC mode. Mach4 is not controlling the height.