Rick - ISO Sensitivity auto depends on the exposure mode you're using. In Program and, I think, Aperture Priority modes, ISO isn't changed until the exposure gets to the extremes of either end of the shutter speed range - normally 1/30 - 1/4000.
You can set ISO manually by pressing the ISO button on the back of the camera and rotating the Main Command Dial to the ISO you want (viewed on top LCD or rear screen when info activated).
You can set Auto ISO in the Shooting Menu >> ISO sensitivity settings >>Auto ISO sensitivity control ON (or OFF).
Also note that If the mode dial is rotated to P, S, A, or M after AUTO is selected for ISO sensitivity in another mode, the ISO sensitivity last selected in P, S, A, or M mode will be restored.
Hope this helps!
When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence. - Ansel Adams