Damned Door!

I would start by pulling the striker out completely, get the door to fit the gap first, then lubricate the door latch, and fit the striker to the door. Lift up and down on the back of the door to make sure that your pins and bushings are still tight, if the original bushings were left too long they can oblong the holes in the hinges and create slop in the pins and bushings even if they are new.