Dash/Radio Lights wont Dim when Headlights come on??

[John98ls1]

well i have a 03 tahoe lt, iv owned 3 others chevys besides this and all of them do this except for this tahoe. When my head lights would come on the dashboard and radio lights would automaticly dim, and when the head lights would go off, say cuz it got brighter outside, the lights on the dash and radio would go back to normal. But for some reason these dont do that, i have to manuly turn them down, what gives????