So are you saying that the ring gear is not pulled all the way down on the flange? The 2 halves of the differential case are made to be a press fit, so that is not a problem. Did these 2 parts fot together completely?
IF yo decide to look into a locker take a look at the Grizley locker from Randy's Ring & Pinion. They claim to have fixed some of the problems that the Detroit Lockers had. Let me warn you in advance that they may have drilled the holes for the ring gear bolts too large. For some crazy reason they said that they drill them for 1/2 inch bolts instead of the 7/16 bolts that they should be drilled for. This caused me some problems with a Yukon Dura Grip.