SI33, I think your friend could get caught on this one if he has any service work done, I think the trucks computer will tally mies and show a discrepancy with the odo... But I may be wrong too.

 

I remember with some older cars I had when I was a kid that you could lubricate the cable that runs the speedo etc. There is a fitting that fits on the end of the cable where it disconnects from the tran where you can inject grease into it. If the cable got rusted etc. the speedo or odo would not work or would stop and start working. I don't know if that is done anymore but if it stops again, I would check on that.