Quick update:
I did find out that plain, white, distilled vinegar from the supermarket @ 5% acidity almost always registers 2.4 on the PH scale. I did a quick test of my meter, and it read 2.9. That would suggest that I've been 0.5 too far acidic at every adjustment.
We may have found the final culprit! Will need to verify the slope of the electrode resistance with something a little higher of course. After adjusting my meter, my tap is reading 7.0 (which is not the water I use in my reservoirs).
Maybe I'll bite the bullet, grab a backup cheapo PH meter, and some GH 7.01 solution. Between vinegar at 2.4, and GH solution at 7.01, it should be easy to determine if the meter is faulty or has an incorrect slope.
Thanks everyone. Might be too late, I'll give it the old college try...