Where to get my car's chip programmed?!

I recently installed a high output alternator which cuts on at 900rpms. My stock alt cut on at like 600rpms, so my idle sits at about 600rpms. It's making a horrible noise whenever the new alternator drops below 900rpms, so I need to reprogram the computer to make the car idle at about 900rpms. I've called local performance shops, and none of them can do it (for the v6). I'm sure someone here has gotten a GM vehicle's chip reprogram, so where did you get it done? Hopefully I can just ship the computer off to them, so they can adjust the idle.

-Thanks

What year is it? We can do quite a few of them.

It's an 01'