My father in law has a 00 Dakota with a 4.7L, The truck sat for awhile, then his son tried to put it back on the road. Upon his first drive, he made it down the road a little ways and lost oil pressure. He put a pressure sender in it, didnt fix it. He was told it needed an oil pump, but couldnt find anyone to do it for him so he parked the truck. About a year later, my father in law decided to put it back on the road. So we did the oil pump, the truck ran fine while warming up, and at low speeds. he drove it around for a few day and everything was great. He took it out to get gas the other day, and it went great til he got to about 50mph. Then pressure dropped from 60 psi to 35, then to 0. I REALLY dont want to tell him it needs a motor. Any ideas? Worn crank? Clogged screen? Any help is appreciated.