On my '93 Accord SE I am having an issue with the speedometer registering 10-15 mph higher than the actual speed. It seems to be (more) correct at speeds under 40mph or so, but at highway speeds is very far off.

Occasionally I will see the needle jump downward to what I assume is the correct speed, then later it resumes it's incorrect display. It appears the tachometer may also be off, as it seems to intermittently be registering lower than what I believe it should

I have been told that to correct this, the entire dash or instrument panel may need to be replaced, rather than any wiring/cabling for the speedometer.

Any insights on this issue are greatly appreciated!

yeah the gauge cluster could be deffective or your speed sensor (you might want to check that)

Are your tires still the stock size?