2001 Infiniti QX • 6 cylinder 2WD Automatic •

I am asking this question again since I have not got a clue yet on what to do.
My Car is Infinity QX4 2001 (2WD). Early this week, the gear could not change to low. On Drive (D), it draws and does not pick up as before, though it moves forward but sluggishly. When changed to Reverse (R) you will hear the sound and feel it that it engages but does not move backward. The rev does not go beyond 2000. Same when it is on low gear (1). I checked the automatic Fluid level always. It is a little above the max mark. (Is that too much to cause problem?). Is this Electronic problem or the Transmission is damaged? I want to be sure please because I am been advised to change the Transmission completely. Pls what do you advise.
July 16, 2011.

Suspect low-reverse clutch hub damaged so overhaul or replace

Jul 16, 2011.