2006 Tahoe front differential issues

[Celicacavy]

Hi, I'm new to this forum but have owned Chevys all my life, I have a 2006 Tahoe LS. The issue is that the 4wd is not working, I have checked all that I can think to check, so now I'm turning to you all for some help. When I engage 4wd it sounds and acts like it is in but does not engage the front differential, I know this because I jacked the truck up and tried, the front pinion is not engaged in 2wd mode but does engage for 4wd mode. After checking and finding that out I pulled the front differential actuator when in 2wd mode the plunger is in, in 4wd mode the plunger comes out no problem. I reached into the differential and tried pushing that plunger by hand but no dice, so then I got my 2lbs maul out and a pry bar and tried to move the plunger that way, still nothing, so I am hoping someone might know what it could be, any help would be greatly appreciated, oh and there is no service 4wd message on my dic