99 Yukon won't go into 4lo

[Zachary Poland]

WE had my 99 yukons auto trac transfer case rebuilt 6months ago, and ever since it will not go into 4lo, 2hi and 4hi work fine but 4lo is not working, the shop suggested I replace the accuator on the transfer case, so I did and it's still doing the same thing, it just tries to engage but it can't make it in, even at a roll. The button just blinks and you hear it try to go in a few times, then it just quits and goes back to 4hi Can you guys help.