Diesel giant is a good guy and he would not be selling it if it did not work..
he has really helped me out...

I think the first step is to DP.... then the second step is to remove the injector and let it soak in a parts cleaner... (sever chemical) Then I think the 3rd step is to take them down and have the professional diesel injection service to calibrate and replace nozzels if needed. (this will cost half of a new set)