Transmission not shifting

[Ni2s4s0aSnX]

i got my 240sx ka, auto transmission. and a few weeks after i got it i was driving it and i noticed that the transmission wasnt shifting. so i brought it down to neutral, and went from first to second manually, then put it into drive and it went into 3rd, but it would come out of third unless i did it manually. i checked my transmission fluid, it was good. then i went to advanced auto parts and got some transmission ****, i dont know, it said sort of that it would fix the problem. after that, on the way back to the house, it was fine, it was shifting good. but then, the next day, it was doing the same thing again. what could be wrong with it.

[sanioll]

whats the problem??

maybe you are. you're going to kill that transmission with that crap from advance auto parts.

search for FSM here. download it, and read it.

i say change the transmission fluid, then see what is wrong.

if the auto is dead, you can always do a 5spd swap or get another one for really cheap here from someone.