Yes, the speed sensor causes the speed indicator (odometer) to work erratic and the cruise control will disengage constantly. It is very difficult to see the sensor from the hood or from the side of the tire. The best way is to lift the front of the van and go under in the center. The sensor is above the transmission casing toward the back of the car. You will see a cable that connects to a gray or black connector that goes vertical into the transmission case. There is only one 10mm bolt that holds the sensor on one side toward the center of the van. I hope my directions as good.
Your RPM indicator is not related to the speed sensor. That’s another issue and simple to fix. There is another thread in this forum that describes the issue, so in case you don’t find it, I will summarize it. The faceplate of the RMP indicator is loose from the instrument cluster. This causes the placeplate touches the needle in one side not letting the needle move freely. The solution is to remove the cluster, open the cluster, and glue back the faceplate of RMP. To aling the faceplate, use a pencil two aling the faceplate to the cluster by centering with the two alignment holes. You will see when you dissassemble the cluster.