I just bought a 1999 3500 dually 4x4 5.9 and when driving the RPM gauge goes to 0 and there is no power after that until I slow done to about 30 then the RPMS start working again and I have power.Anyone know what that is

 

Most likely the crank position sensor. It hides behind your injection pump.

 

ya cps probably does it sometimes not start?

 

That is what it was thanks guys