My 99 F150 4wd won't engage. When I shift it the light on the dash illuminates. If I jack it up and have it in 4wd I can turn the tires by hand and it will spin the front drive shaft, when I take it out of 4wd the two front half shafts will spin but not the drive shaft. I believe the problem to be in the transfer case. How hard is this to fix? How long do yall think it will take?

I just had 4.56 gears put in it. anything with that could be causing some problems?