How much of a difference is it? Going up slower than down is normal to an extent. The weight of the glass versus gravity slows it slightly going up. Going down it's just the opposite.
2014 Mustang GT custom ordered to replace the GT500: Sterling Gray, NAV, Recaros, Brembos, Glass Roof, back up camera, 6 speed auto, loaded
2012 Focus Titanium - 18" wheels with handling package
2009 GT500 Shelby (700 rwhp) - sold