My dad has a 2001 3500 that he bought wrecked and salvaged. It only needed some body work. He's been driving it - went on a trip from OH to MT, and just came from OH to see me in NC. He's had a problem with it occasionally running rough and having no power. He thought it was problem with low lubricity in the fuel because it would smooth out if he added a quart of oil to the fuel tank. Now, though, it looks like it's really a rough road issue. It runs fine if the road is smooth (new pavement) but rough roads (even highways) make it miss and lose power. He did add a fuel pressure gauge and the pressure doesn't drop, which seems to rule out a lift pump issue or pinched fuel supply line. Any thoughts on what the problem may be?