How did you go with this?

My bunky 97 GX foz has just developed a speedo prob. It is an electronic speedo. When I first get in the car it works ok for the first few minutes whilst still cold. As it warms up, it starts to fluctuate with about a 20k variance. After about 5 minutes or so (travelling at around 70km/h) it bounces from zero to 80 and then sits on zero. After it has been on zero for a while and I slow or stop, I often get the check engine light.

Does this sound more like a speed sensor or the cluster?

/csb.