1998 blazer wheel problem

1998 blazer 4wd the right front passenger wheel won`t rotate backwards, when in reverse it stays locked and drags across the ground,it rotates forwards but makes clunking noises.
i replaced the hub and the half shaft 2 years ago. is this a transfer case problem or a hub problem or a half shaft problem?? or some other problem?

It sounds as though the front axle is acting up. When you put it in 4wd, the transfer case activates a vacuum switch which supplies vacuum to an actuator which pulls on a cable to engage the front axle. This engagement happens on the passenger side of the front diff, in the passenger side axle tube. If, for some reason, the collar inside the axle tube is not connecting or not disconnecting properly, it could cause the symptoms you are experiencing.