Nissan Repair: transmission computer, nissan maxima, valve body

Question
Von my friend owns a 2001 nissan maxima and just replace the engine which was seized because it ran out of oil. She also complained the the transmission would periodically give a problem like it slips out of gear and she would have to put it in neutral then back in gear and it works. Now when then engine was swapped the mechanic didnot dismantle the transmission from the old engine he put the one in the came with the engine. The car is doing the same problem with the transmission. Does the car a specific computer for the transmission and where it is located in the car or you want me to read the codes. should i read it with the engine on or off. with it on do i need to shift the gears through. Please help as usual.

Answer
Kingsley,

The transmission computer is located on the transmission close to the valve body.  It is really a black box. Nissan had a problem with the computer on the 2000 and 2001 Maxima automatics.  Mine had the same problem.  It was the shift computer.