I have an 04 Trailblazer that I'm having problems with. I can shift it into 4 high, A4WD, but the front tires never engage. I hear the actuator engage but the tires do not go into 4wd. However I can shift it into 4LOW and it works just fine. There is no service 4wd light on and everything else seems fine. Any ideas to what this problem could be? Thanks for the help..