The attitude monitor I can see as it has to be hooked to the Juice in order to work. The Bully Dog Outlook will work as a stand alone unit so I don't see how it could cause any issues. Same with the Quadzilla Commander.
True, however a set of gauges is not perfomance enhancing. Infact, it will help keep from overworking the motor. As long as you use a stand alone guage kit like the outlook or Quadzilla, that will operate without a chip or programmer on the truck you should be fine.