Name only. They changed the nomenclature about '91(?) to better indicate what the transmission was.
4 - number of forward gears
2 - torque capacity
R - Rear wheel drive
H - Hydraulic control
Based on that, makes sense that an 46RH matches up with the A518 since the "6" indicates a greater torque capacity over a 42RH which is an A500. There is also a 47R_ and 48R_, not sure if they are "E" only nor if they bolt to a 5.9 since (I think) they are diesel only.
The "E" means they changed to an electronic governor control. Functionally, it removed the weights (governor) in the tail housing and the PCM monitors hydraulic pressure in the governor circuit and controls a solenoid to cause the pressure to rise as required.
BTW, I've gone looking to find out if there is a 43RH/43RE or 44RH/44RE, but never found anything conclusive. Maybe it is a Grand Cherokee trans? Not sure. Either way, I thing the generally excepted nomenclature is 42RH or 42RE.
Not sure on the 2 pin and 3 pin thing. I wouldn't be surprised if a 46RH is always a 3 pin, but an A518 could be either. But that is only based on the idea that by '91 when the nomenclature changed maybe they always had LU? No idea.
