Ok sooo since I know this question is posted seriously I will try and give you a serious answer. First off a 2X4 is a piece of wood, so I'm thinking you have a 4X2. Secondly you pretty much just answered your own question by saying you have a 2 wheel drive. That front diff of yours is non existent.
Gross over-simplification warning:
So the differential is used to distribute power from the engine to the wheels. The engine powers the drive shaft (lets not get into the transfer case here) which is connected to the differential. The differential distributes the power from the driveshaft to the two wheels. In a 4x4 the engine powers both a front and a rear drive shaft to turn all 4 wheels. In a 4x2 the engine only powers one drive shaft that (in the case of the X) turns the rear wheels. So in a 4x2 there is only one differential to be found.
Thanks for the support and not laugh a newbie off the board. I was really embarrassed. But, I am sure that there are some guys reading this that are breathing a sigh of relief. They are glad that I asked the stupid question instead of them. There are guys like me who are truly new to this stuff but are eager to learn.
The X is my first truck. I've not even heard of "T-case" until I read about it here (Yes, I know. I don't have one. Hehe...). And I had to google "RTV" to find out that it stands for "room temperature vulcanization". I've learned a lot from just reading the board. My first oil change on the X was a disaster. I had oil everywhere. But, I am happy to report that I just did my seond oil change and I didn't spill a single drop on the ground. Not having a front diff is a blessing, I guess. It makes changing the diff oil that much easier. LOL.