If I remember right, the earlier ones had it mounted behind the front bumper, but in later years, they moved it to on the block to save a few bucks. I also believe that it is also related to the "heavy duty" package. THe heavy duty package has an oil "cooler" added to the truck, where a truck without this package more than likely has the filter on the side of the engine.
I use the "cooler" term loosely. Essentially they are flowing engine coolant through a box that the oil also flow through on the other side of a metal divider. But, keep in mind that the cooler lines that the coolant flow through are both on the same coolant hose located 4" apart. So, the amount of coolant that flows through the cooler is very minimal. So, the cooling is more of a "feel good" thing in my opinion. Once I saw this, I removed the remote oil filter assembly and went back to mounting the filter on the side of the block. It isn't that bad, just have to learn how to lay on your side, reach up through the suspension with your left hand and out it comes. But then, having the lift and big tires on my truck makes it a lot easier. I'm also the one that drains the oil directly into a 5 gallon gas can via my check valve drain line I have on the oil pan.
