I have a 2004 HO, with auto trans and a optional high idle installed by the local Dodge dealer here in Fairbanks, Alaska.
The factory high idle isn't enough, and will only idle up to approximately 1000 RPM. I have an after market high idle installed that can be set above 1500 RPM, not that I would ever set it that high. I usually keep it set to 1200 RPM after the truck has warmed up some. It works great, just turn the adjustment knob to the desired RPM setting and push the button to engage or disengage the high idler.
You can also release the high idle by momentarily tapping the brake pedal, at which time normal idle takes over.
It is made by a company from Canada, and IMO is one of the best and most reliable high idlers on the market.
It is the only one that is used in our extreme climent with temps down to -50 degrees in the winter.