I have a 2000 PSD with 66,000 original miles on it. In the last month when the engine is cold I get a slight RPM surge at around 40 to 45 MPH. It doesn't do it any other time. Once the truck warms up it stops. This truck has been garage kept and all service as been strictly by the book. Transmission seems to be shifting with no problem... Any ideas? Transmission was compltely service @ 43,000 miles. Your response is greatly appreciated in advance......