Dave,

There are a couple of aspects of your posts that are bothering me.

You keep talking about changing the shutter speed, but if you are in Aperture priority mode, you can not change the shutter speed from what the exposure system sets unless you change the aperture or ISO. And in either of those cases the EV remains constant and the histogram won't change. In A mode, turning the main (rear) command dial has no effect on shutter speed.

Also, you mentioned "watching the meter." In Aperture priority, the meter in the viewfinder is usually not visible as long as the camera can set a "correct" exposure. The only time the meter appears in A mode is when you press the EC button and/or dial in some exposure compensation, or the camera can't set a correct exposure.

If I understand what you're wanting to do--push the histogram to the right--there are two ways to do so if your preference is to set a given aperture. One is to use A mode and dial in some + EC. The other is to use Manual mode, set the aperture you want, and then dial in a shutter speed that gives a measure of + exposure as indicated by the meter (which is always visible in M mode).

Hope this helps.

Kent