Tonight I took the complete valve body that was on the used transmission that I bought and installed it in the car. I also put in a new oil filter and swapped the rev sensor too while at it...
Transmission does the exact same thing as before :/
Either the TCM is fried or it's a mecanical problem in the transmission...
The only thing I find weird is that the transmission still goes from 2nd to 1rst whitout any reason, as if it had no reference of speed or "power demand"... If it wasn't for that, I'd bet on a mecanical trans. problem...