Having to fit a guide rod seems a bit strange. I'm wondering if the new guide rod was out of spec or maybe the inside of the slide ? Did you check both with a micrometer ?
Secondly, you may want to fit a match barrel bushing before installing a match barrel just to see the difference. Also, fitting a slide stop and correct link pin will help with accuracy. You could be surprised depending on the barrel specs.
Keep us posted on the progress.