d30 posi-lok issues!

i installed the 4x4 posi lok just a couple weekends ago along with a new aluminum fork..bad choice by the way..spend the extra $20 and buy the cast one on their website. anyways..it took some adjustment right away but then everything worked well . i went out this weekend and when under load the fork would disengage and it would "pop"out of 4wd ? when i installed it everything else seemed to be in good shape. i am going to see if anymore adustments are needed but i don't understand why there would need to be..it worked great for the first couple hours of wheeling. i am going to upgrade to the new cast fork also. the collar and axles seems to be in good condition..?? anybody else have similar problems?? what's causing it to slip out of 4wd?? thanks