4R55E vs. 5R55E
The 4R55E is a four speed, while the 5R55E is a 5 speed. Both transmissions are electronicly controled (the same transmission with mechanical controls is a A4LD). The easiest way that I know of to tell from the outside appearance of them is that the 5R55E has a output speed sensor located at the aft end of the case, while the 4R55E has a input speed sensor only. Internally, the reverse drum of the 5R55E has squares machined out of it for the output speed sensor, while the 4R55E reverse drum is smooth. Both the 4R55E and 5R55E have 6 stators on the planets, if you have only 4 stators (although there are 6 stator positions), then it is a 4R44E. Hope this helps to clarify.