The unfixable mystery problem

[GettaRobo]

I have an 88 n/a auto supra from california, that has all the extra sensors and other goodies, with a faulty speed sensor. Other than that, the car runs fine except that if you floor it, the car will rev up to 4000k and then stop and not go any higher. If you push the pedal down 3/4 of the way, it will rev above 4000 up until redline. I have the car in at a mechanic that has knowledge of these kinds of cars. They've checked the fuel pressure, the distributor, they looked for some sort of rev limiter, they've looked for vacuum leaks, and nothing. I have no more ideas (nor does the mechanic) of what could be wrong on this car and it's really starting to frustrate me. If anyone has any clue as to what could be causing this, I would greatly appreciate your input. Thank you very much!

P.S. I have another car that is the exact same as this one from Canada that I'm using as a parts car. The mechanic suggested I get it towed there for random part swapping and I'm thinking I will have to resort to this but I'm hoping not.