Just an update in case it helps people down the road. It was something faulty in the Speedometer/ gauge cluster itself. Dave0430 hooked me up with a replacement and that solved the problem.
One other thing that might help people in the same situation, the odometers are easy to swap out in case you get a new speedo unit but want to keep the same mileage on the bike, it's just two little screws on the back of the plastic housing, and then two more to detach the odometer mechanism from the small electric motor that turns the odometer dials. Changing the numbers on the odometer itself, as far as I can tell, is virtually impossible without irreversibly damaging the odometer mechanism.
Thanks for the input everyone.