I have a 98 MPV. The cruse control works, but pulsates. At 40mph it's ok for a while. Over 45mph and around 60 mph it slows down and picks up and slows down. It seems to be ok when first engaged and after a mile or two it starts. Any ideas

 

Inspect /clean the VSS and all connections to it. Inspect/clean/lubricate the cables to the throttle. Clean the throttle body. Inspect the CC-motor.
Check the throttle position sensor.

I hope you run across the actual cause of the problem when you do these things.