Nissan Repair: Shifting Problem [Continued], speed swap, gunky

Question
"Hello there,

Brief overview : I have only seen this problem once on this boards and it was not solved, give it another shot. I purchased a 93' SE coupe that had a shifting problem, figured i'd luck out and it would be an easy fix : WRONG.

The transmission shifts when it HAS too , not when it's supposed too. IT shifts at 6k revs everytime; no matter what gear. Now i went to the local mech and was told it was either speed sensor or solenoid , so to save money and tackle both cases i purchased another tranny that i knew WORKED, although the problem still occurs.

Now i than assumed perhaps it could be the speedo , it's a HUD and since i bought the car is had dimed in and out ; but i have seen it work. Therefore i'm going to give it a shot tom (i have analog) but i don't think it will solve my problem.

Although 5-speed swap has been in the back of my head the funds are not readily available at this time and basically want a daily driver "

"Update:

So i swapped my cluster over to analog , speed displays but does not fix my problem.

I also unplugged the TPS ; it would default and work if it was malfunctioning | It remains unplugged as im cleaning the contacts (GUNKY) but i doubt that will solve the problem.

Im pretty stumped at this point , could it be the speed sensor?

Im just frustrated and im not to fond of dropping money on a local mech , considering they have mis-diagnosed 2 times already .."

Any last options Von! [240sx]
Thanks , Sebastian

Answer
Sebastian,

For the transmission to shift at such a high RPM would indicate that the governor in the transmission is plugged up and sticking.  I would remove the transmission governor and clean it and the passages to and from it and reinstall the governor and check shifting.  I use Cottman Transmission and have had good luck with them.  They could do a diagnosis for little or no money and let you know for sure before you proceed.