1999- 5.9L Air Dog Fuel Unit
 

1999, 5.9 Cummins starts and idles good but runs very rough when I speed up. Waiting on pressure gauge to check the Air Dog FP100 fuel unit. A couple quick questions:
1. I changed the fuel filter but only drained the seperator. Should I have changed it?
2. If it is the pump can I replace just the pump or do I have to change the whole unit?

Any help will be appreciated. Thanks