Ok so... first, a little back story... my uncle who passed with cancer about a year ago gave me his truck, and he has had it since I believe 92. I was told that it was kept up with and had the oil changed everytime the sticker date came up. (I cannot prove this because I did not own the truck) he was having problems with overheating and would use hose water to fill the radiator (which is why I flushed the radiator and filled it up with antifreeze) as for the oil filter I looked it up myself at autozone and made sure it was the same size as the previous, however I did not prefill it with oil before I replaced it, I did lube the gasket with the new oil though. The oil was penzoil platinum and was said to break down most engine sludge within the next oil change, I should have read up before jumping headfirst to the synthetic however I didnt. Also the oil filter was just a fram high mileage oil filter, I couldnt give you a part number right now however. I do agree with those of mentioning something about the oil pump, it makes sense and seems to go with the issue, but I have not checked as of yet. Last I heard you have to lift the engine to pull off the oil pan and to check the oil pump, I do not have an engine lift or a mechanic friend to do this so im not sure how to check the oil pump.