2001 Chevrolet Blazer • 115,000 miles

My 2001 blazer has a service 4wd light that comes on after driving for about 5 min then when I shut off the engine it goes away then comes on again after 5 min driving I can switch it to 4wd auto and it shakes when I turn but I can't get it to switch back to 2 hi unless I unhook the battery I have checked all the vacuum hoses and they seem to be fine nothing disconnected I also serviced that front and rear diff and the transfer case and didn't see anything out of the ordinary I recently changed the front brakes and had to replace the abs sensor don't know if that has anything to do with it
Please help I need to know what direction to go with this
October 26, 2012.

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