hi,i had this problem on a sierra,i was converting it to electric from manual,what happens is the splined shaft wears and 1 of the wires(theres 2)jumps a couple of teeth which makes 1 side open before the other,once they are like that they are gubbed as theyre not serviceable,to remove your 1 pull the sunblind back,and look at the front of the sunroof from the inside,there are 3 screws,remove them,then pull the metal surround back out of the way,then look up at each side of the sunroof,in the darkness theres 3 screws that will need to come out,4 should be no probs but the 2 front ones will be rusted to bits,either get a twist socket which will bite and remove them if you are lucky or get rough with it as its probably fxxked anyway!