OB Mechanics assemble ( transfer case)

I have a borg warner 4406 4l34-b. it is on a 2004 f150. 4x4 disengages under high rpm's. I took it to a transmission shop and they replaced the high low range selector. Problem kept happening. Took it back and they put shims on the shaft said it had to much slack. Problem still exist. I replaced the shift motor and the coil on the inside and the problem still exist. What could be wrong with it. Works in low rpm's. But when you get the tires to spinning it kicks out with a loud jerk.