I have a 4" service duty XD 45. I bought it used from a local gun dealer for what I believed to be a good deal. I have put probably 600 or so rounds through it. I can pull the slide easy enough but I mean its rough it's not smooth like I think it should be. It's a very stiff slide and anyone that shoots it says wow that's a hard slide pull. I was wondering what kind of internal upgrade would help with the slide pull.