9" Ford Problem

[CoMax Racing]

I have been having a problem with a 9" Ford I am setting up. I install the gears with proper pinion depth, lash, pattern etc. Preload the bearings, tighten everything up,road test it. I remove the carrier to inspect the gears and discover the lash has increased by about .008". I have done Ford diffs before and never had this problem. The bearings must be moving but I pre-load them. I am stumped.

Any help would be great