rear diff moove in bulkhead ???????

I'am to rebuild my 3.3, and yesterday i've put new diff and new bulkhead.
In the front, the diff is very tight fit in the bulkhead, fit perfectly, but in rear, the diff have lot of free play (up and down when i take the output with finger and try to moove it up and down).

The little plastic pin who snap in the frame to block the diff moovement in the bulkhead is brand new, try to re-install the hold bulkhead, but nothing to do, always the same problem.

is somebody have this issue too or could give me somes tips

Thank you!!!

David