The "difficulty jumper" only adjusts the time the ghosts stay blue, afaik.
Your problem is the clock is running too fast. It could be a hardware hack or an issue in the clock circuit. I had a board doing the same thing once and it was just a shorted lead on the bottom side of the pcb.
I have come across the hardware hack a handful of times. It was how they used to speed them up before the speedup chip was made.
On my pac-man, it did make pac-man move slightly faster initially. When I undid this, god it was slow. Also, the patterns i was reading up on did not work at all, but after removing the mod, they work great.
