pressure

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My truck has been a great truck but a minor problem has occured.It began running really rough in the lower gears(manual tran). Now it is getting worse.I have changed the fuel filter and the injector.Now if It won't start I can turn the screw that holds the injector in place and it will spray fuel. It will then run.I was wondering if maybe the fuel return line could just be plugged or if it is the regulator. It just seems to have to much pressure until you are going down the highway.It does this everytime it is driven now. Help Thanks