I personally would go to your local parts store and buy a hardline guage...meaning i would purchase one that has a copper tubing line that will actually flow oil through it to the guage and see what it reads before i would get to concerned. If your pressure is dropping to 0 then i would take the time and spend the money on a new pan gasket and drop the oil pan and check the oil pickup tube to see if it has cracked or loosened. if that is not the case then i would look at the pump itself before i drop huge money in it....you can also drop one rod and one main bearing cap and use plastiguage in it to check for clearences and visually inspect the bearing surface to see if they are showing any signs of oil starvation.

Sorry so long winded with the post but i have done this before on alot of different engines and found that its saves alot of money and time .

 

could be a collapsed oil filter or bad pick up tube

 

I would go to the store and get a mechanical gauge. I am putting my money on the pick up being broke or set to high. The truck idles with good pressure goes down the road with good pressure you stop oil runs to the front of the pan and you lose oil pressure. Is the truck 4wd? If so it takes 10 min. to take the pan off and check the pick up.

 

Fram filters are notorious for collapsing internally, especially on diesel engines where they get rode hard and put away wet. I'd replace it immediately and see if that changes anything.

Then, cut the filter open and take a look inside. Post pics... I've cut open about 50 Frams of every type (extra gaurd, etc.) and they are all basically the same -- a small amount of filter material, a pair of cardboard end caps, sloppily glued on, a thin strip of metal that is supposed to be a spring, and a mal-formed rubber check valve.

The K&N filters are good, as are the Mobil 1 (same filter inside the housing) -- both are synthetic material with good construction. Wix are also good filters (NAPA Gold are made by Wix). Fleetgaurd is also a great diesel filter and are made to withstand the rigors of diesel engines for long-term use.

After that, the advice offered by Death85e is right on the money.

 

well i drained the oil to get ready to drop the pan and only about 3 quarts came out. som idk if i was on a slight hill when my dipstick read full or what. so i changed the oil used k&n oil filter and now my oil pressure ROCKS! so any who i go to start it and a connector on the end of my power supply to my starter broke so i chnged it and went to put it back on and the starter silinoid broke when i tightened it on. so had to pull it buy a new silinoid change them out, and now everything works fine! so releived . thanks for all the advice guys!