Can I use the moparmans high idle switch with the quadzilla xzt? I want the 3 cylinder high idle for my truck. 

I do not think so, the switch fools the sensor to make the ecm think it’s actually colder than what it is to turn the 3 cyl high idle on, it’s actually already a feature in the ecm from the factory

So why would the switch not work? I’m not understanding your answer sorry. 

As long as your truck is flashed with the TSB for enabling high idle, and you turn off Quadzilla's high idle feature, then yes, you can.

Yea you can,  just dont use the quadzilla high idle a long with the ecm high idle.