i am not gettin much air blowing through most of my vents even when fan is on high. only one with much comin through it is the one to the right of the stereo. i have tried opening them all and have tried closing all but one or two to see if that makes a difference and it does nothing noticable, in fact actually flows a little better with all of them open. anyone else have a 99+ silverado or know if this is normal? if so is there anyway to make the other vents blow more air?