transmission problem 1985 300zx turbo
 

Ok before i get started i should say i have searched forums first! I just recenlty got my tachometer working correctly and i have noticed that when i am roughly around 65 i am running around 4200 rpms which is kind of high. I have also noticed that it is only shifting into third. DO not kill me for having wrong information as in someone saying there's only three gears dumb a or something but could anyone tell me what in the transmission is screwed up if i wiggle the automatic a little to N-neutral and it doenst shift out still

The transmission fluid has to reach a certain temperature before it will shift into 4th/OD.

There could be a few problems:
- power/OD off switch pushed in.
- temp sensor dead or disconnected.
- transmission is FUBAR.