After looking at some oil and oil filter studies, weighing price and performance, i settled on mobil 1 full synthetic and I use either the mopar or napa gold filters. I believe those choices get you 95-98% of the benefit of using good filters and synthetic oil, so I don't bother springing for royal purple or something else expensive, though some guys swear by it.
Also, to continue on with what hemigreg was saying, for a used truck, if you are switching over the oil to synthetic, running some seafoam or marvel mystery oil to clean up the engine, running star tron to clean up the fuel system, etc.., just be sure that you keep an eye on things such as oil level/color, spark plugs, etc. Cleaning all that gunk out of your engine/fuel system is good for your truck but you may need to add oil between changes or change more frequently, and if you clean out the fuel system you will likely need to do the plugs once you are satisfied that you are "clean". Some food for thought.