I'll assume that you have been on a 10-speed bike at least one in your life. Do you remember how the front chain had two rows of teeth (gears) and the rear wheel had 5 rows of teeth (gears)? The overall gear you were in depended on the combination of front and rear you chose. Think of the gears on the wheel as the transmission (5 gears equals a 5 spd transmission) and the front gears as the transfer case. On a bike, the larger the gear on the front the harder it was to pedal and on the smaller the gear on the rear the harder it was to pedal. The basic idea is that the more times the pedals go around compared to the rear tire the easier it is to pedal.
The transmission and transfer case do essentially the same function as the two sets of gears on the bike for your truck. Each time you upshift the transmission you give the engine less leverage (1st is 3.93 to 1 and 4th is 1 to 1) on the rear tires which is why you need lower gears to climb hills. The difference in gearing in the transfer case provides the ability to drive the front tires (4wd) and also another lower range of gears. The stock transfer case low range gearing is 2.28 so going to 4.7 provides almost double the leverage for the engine on the tires.
Make any sense or am I just typing to myself?
