Did you buy the truck new? If not, a previous owner might have installed a aftermarket fuel filter in line from the tank to the factory filter under the hood. I did that on my '06 in order to get the Cummins mandated 4 micron filtration they spec for this engine.
Look under your truck, along the frame on the driver side, between the tank and the driver seat area for an after market filter. (I presume a filter under the hood would have been obvious.)
A truck with those miles might have a filter that is blocking flow if it's not been changed because you weren't aware a past owner had installed one.
