speedo has been fine untill today. when you start the engine speedo does its diag ck fine but stays at 20 mph all the time ?

Sounds like a dead battery in the sending unit. Do a search and you will find a thread that discusses it. You can send the sender to Livorsi and they will put a new battery in it. As I understand it the cost is about $100. One guy in the thread replaced his own. He got battery from batteries plus for about $4. They put the shrink wrap on it and soldered the leads from the old battery on it.