Help 2003 f250 diesel
 

I have a 03 f250 6.0 the truck idles good and drives some what ok up 25 mph but then stalls and falls on it's face then it stalls after 25 mph then hard to restart fuel filters are new and drained and cleaned, oil is at full mark, fuel is fresh, new alternator the old was putting out under13 volts can anyone help