Popping out of 4h

I have an 86 trooper with part time 4 wheel drive and automatic hubs. It goes into 4h easily but will pop out to neutral when under power. I have gotten two opinions on this from 4x4 friends. One is that the hubs are bad. The second is that the transfer case has a problem. Any ideas? I appreciate the help.

if you have a manual trany there is a spring inside that pulls over on the shifter. if it is missing or put back wrong (easy to do) or the spring is weak then... I had the same problem on my 87. no big deal. the cluster gear went bad on mine and i replace the tany w/ a used one which had a good strong spring.
make a friend hold it in gear, it's cheaper!!