climate control blower

I just noticed this and do not know if it is normal. I have a 1996 Cherokee, 4.0l, automatic, 4x4.
With the selector set in the vent position and going on a flat stretch of road the air come out of the dash vents and the floor vents.
However, when I go uphill the air shifts to the floor vents(90%) and the dash vents (10%).
Is this normal/correct?
If not, what should I check?
Thank you

Check the vacuum canister behind the front right side of the bumper and follow the line as it passes under the battery; the battery often causes leaks that will do this.

I know this is old, but still have the issue.
how does this cause the problem?
I did trace the lines, but found no leaks, kinks or funny looking things.

Common problem. Had it happen on my old 93 ZJ, and it has happened on my current Jeep. Both problems (in my case) were attributed to cracks in a vacuum line. As mentioned before, it may be the vac cannister is bad, but if you look at your engine bay from the front. Look tothe passanger side where a bunch of vac lines come together.
There should be one that is light gray in color. Inspect it very closely. That line is the one that caused me all of my "vent/floorbaord/defrost" ghosts....both times. Just found the tiny cracks, cut out the the part that was cracked and spliced in new line. Problem went away.

If you want, you can get a can of carb cleaner and spray it on the lines (very carefully!! so as to not overspray onto hot surfaces), if the engine revs up momentarily, then you have found a crack in the line.

Hope this helps.

James