What you describe is pretty normal, it'll take a while to get the weatherstripping to take a set. It has to be overly tight and to force itself into shape. I find i have to let out the striker a piece and then readjust over a period of time as the door closes tighter and tighter, when all is done proper that is when you get that 'chumpf' when the door closes and everything should happen in a single sound. A difficult thing to do.