The issue is two-fold...

The engine starts fine and idles smoothly. But upon acceleration, a)
the car will stumble/lurch and lose power, and b) the speedometer
needle will bounce and/or bury itself. A drop into neutral and the
speedometer reads actual speed normally. The two problems began to
happen simultaneously; one did not start up before the other.

Any ideas on what could be causing this problem? (Something
electrical?)

Thanks,
Brian