Truck Repair: 2001 N14 Cruse Control, cummins n14, faulty sensor

Question
I have a 2001 Volvo 660 with a Cummins N14 red top. When it gets warmed up after about 10 miles of driving the cruse control will not hold speed the truck slowes down fast and the pto high idle will not keep the rpm's up. I had it in a local shop today and they said it may need a ECM reflash I think it may be a bad ground what do you think.
Thanks
Cliff  

Answer
If the cruise is cutting off then it might be a switch or sensor problem.If it will run fine on the pedal than it might be the VSS sensor not reading correctly due to the yoke on the trans loose or faulty sensor.The VSS can go out & not log a 241 fault or if the speedo gear is slipping then it would not show a fault because it is reading MPH.The default parameter W/O VSS is usually  around 1400-1500 RPM unless someone set it different. Oh yea,a recalibration probably will not fix your problem but if there are alot of changes(updates) then it might not be a bad idea if it has more than 5 updates or a changed calibration due to updates.