EBP Valve issues...
 

I kno im late on this but how do i fix the Exhaust Back Pressure Valve??

What do you mean fix? What's wrong with it?

It's on my dads truck, but he feels a loss of power and worse milage and it's doing the open closing thing like as mentioned before

Try unplugging the EBPV. It's a connector under the intake side of the turbo... I think there are two wires that go into it. I forget.

Two wire plug on the bottom of the turbo pedistal, you can unplug it. My guess would be a plugged EBP sensor.

Where wud the sensor be??

There is a pipe that runs from the exhaust manifold to the front of the engine. The sensor is in the end of the small pipe in front of the timing cover. It could be the pipe or the sensor that is plugged. Check and clean both.