rough idle after engine gets to operating temp.
 

2008 F 450 6.4
engine runs great cold, after it runs about an hour, it still runs great at higher rpm,
but idles rough.
i get an error " low fuel rail pressure" occasionally
i have put in new filters, new lift pump and new crankshaft sensor.
still same problem
Any help would be greatly appreciated.

If anyone else has this issue.
It was the fuel rail pressure sensor.