I need advice about tuning a guitar

You’d think after 15 years I’d have it sorted out.

No matter how well your guitar is set up and how nicely you fret the strings you are still placing a slight stretch on the fretted string. That means that you have to compromise with the various open chords as they use different combinations of fretted and open strings. For some reason I’ve always been able to clearly hear this when I’m playing but if I listen back to a recording of myself, I don’t notice it. It may be something to do with being physically attached to the sound source.