axle problems w/ lifted 99 chevy

I have a 1999 chevrolet 1500 truck. I had a 6" skyjacker suspension lift put on it. The first time I locked it in 4wd the front driversside axle popped out. I had it fixed, but it done the same thing and busted the housing when I locked it in 4wd on the second go round. Do you have any suggestions on what I could do to fix this problem or is there a special lift kit I need to keep the axle from popping out.