Well, I was about to order a speed sensor until I was driving to San Jose from Sacramento today and realized that the odometer indicated that that I had only travelled 30mi... but I know I had driven almost 100. The entire time my speedo was reading 110mph (or thereabouts) when I know I was only doing 70-75.

Cliff's Notes: Speedo reads too high at random, odo reads too low at the same time.

I'm thinking gauge cluster here. Any suggestions otherwise?