Todd &Autumn,
Electronic tachometers are typically +/-5% of full scale devices. You could have used the tach while you were on the dyno (using the dyno tach as a standard for comparison) to quantify it. However, you can use an MSD ignition tester to quantify the real numbers fof both tach and shift light.
The process only takes a few minutes and doesn't require running the engine, using a test spark plug.
The g meter indication on the race pak can also give you lots of info on shift points as when the g is at peak in each gear so you can relate that to RPM for solid reference.
Good Luck in your testing process. Takes a lot of passes, but worthwhile when you take good notes and narrow solution paths.
Regards,
HB2
Dissident