Hey Eagle33 this sounds like a problem I had on my 92 SC4 about a couple of months ago. I did not use SeaFoam (yet) but I was driving down the highway at around 70-80 MPG when I looked at my gauge and both my RPM and Speedometer were 0 but after a few miles everything is fine and has ever since. I don't know what happened but so far so good it hasn't happened again...