Nissan Repair: Nissan 240sx Shifting Problems, nissan 240sx, minor setback

Question
Hello there,
I purchased this car at a great price with a minor setback. The car did not "know" when to shift, therefore it always shifts around the 6k range. With that being said i already visited a couple local mechanics , most of them said it was a problem within the transmission ( solenoid or speed sensor ) so to cover all the possibilities i went ahead and purchase and installed another transmission; unfortunately this did not solve the problem.

I have a 1993 SE , this models includes the H.U.D , since owning the car it has no worked ; it tends to show it sometimes but lately it has been a no-go. This is a coomon problems with these cars but the side-effects are never a shifting error. Tonight i will be swapping out my digital for an analog speedo. I am not keeping my fingers crossed and am at a desperate situation.

What else could potentially be the problem?
Most cars have an ECU ; does this car have an computer for the transmission?

Answer
Sebastian,

Wow, I love your car.  First, the computer receives information from a couple of sources to shift.  First, there is the TV cable and if it is not working the car will shift strange.  Second, the manifold vacuum and third the computer picks up the speed at the instrument cluster.  I would take the cluster out and clean the contacts on both the harness and cluster using a number 2 pencil eraser.  Blow off the dust and reinstall.  Most of the time this corrects the problem.  If not, check out the power distribution block on the cluster.  It might need to be replaced.