I have 99 LTZ with the 3.8. mine idles at about 800 with nothing on.
I had some idle problems with mine, and it comes and goes.
Maybe change the plugs and wires. Check your coils.
Where do you live? I live in Chicago, and in the summer they have some reformualted gas here, and the mechanics says its hard on the injectors, and reccomend injector cleaning or running seafoam thru system.