I did the abs speedo thing already. Replaced the rear sensor about 1.5 years ago and it worked well. At that time the speedo was just kinda jumpy both ways. I have also replaced the speed sensor on the transmission.

Now it is intermittant and jumps way to 100 mph and back down. Cruise control is also off. It too is jumpy on hard one second off the other. I do not have the abs lights on so I don't think it's that same rear diff sensor again.

I've read other reports of this same problem but they are not conclusive. I'll post the fix to this if I could get some help on this one.

 

Try the ignition swtich, not the lock cylinder, the electric ignition switch. I know it doesn't sound right, but it has been the cure for many problems identical to yours.

 

Has anyone else had a speedo problem related to this? I can understand how it would effect some things like blower motors that I found when I searched it, but before I go throwing parts I'd like to know if/how it actually could effect the speedometer.

 

I had the same problem but also my tach was acting up. i fixed it with the crank shaft position sensor behind the starter...