42 is for V6, 44 is for 5.2, 46 is for 5.9. The internals get bigger with each step. The 46's rotating assembly weighs significantly more than the 42's so that there is not as much power absorbed in trying to turn them. The less power it takes to turn the transmission, the more can get to the wheels. As far as I know, all the output shafts are the same, so the transfercase should be universal, just change the transmission. What does matter is that it's easier to just find a 4x4 44RE so that you aren't swapping tailshafts and tailhousings off a 2wd 44RE.