lost 4wd ,...that was the first thing i replace from gm is the dash switch. replace encoder motor from junk yard with 1 year warrenty, that did not work. so i drain fluid to find minute metal,pulled transfer case found clutch thrush bearing wiped out clutches worn,ect.replaced transfer case and now 4wd drive works but went i put selector switch in 4wd position the encoder motor makes noise and light flashes on switch then light comes on auto4wd on selector switch even though switch is in 4wd position 4wd is working while in that mode. all other selections work fine?