2005 4x4 delayed engaging?
 

I have a 2005 f150 XLT that usually won't go into 4x4 when setting still. If you put it in 4x4 low or high it sounds like the shift motor goes in on transfer case but 4x4 won't work. If you drive down the road a ways it will usually go in (but not always). This is vary unhandy if your stuck. Front vacuum hubs work great engage and disengage every time. Tried a new shift motor on transfer case same results. When it's not working front driveshaft (from transfer case to front differential) is not turning. light on dash always comes right on even though 4x4 is not really engaged. Any ideas? I know 4x4 issues seams to be a common thread but haven't been able to find one that 4x4 works after you drive down the road? I have tried engaging 4x4 in Park, Drive, Natural, Reverse, rocked the truck back and forth but just won't seem to go in. Tonight after getting pulled out drove 1/8 mile down the road and it locked in on its own.