Help

[MauricioPinto]

I have a 500SEC,wen i accelarate to start moving i feel vibrations, the car moves slowly, the garage tall me that was the torque, i have change it with another gearbox, but now i have the sensation that sometimes the 1 gear is not in action, the car moves with vibrations and no power at all, but the engine as no problem.
Another thing wen i accelarate in a freeway, if i made a strong accelaration i feel again like the gearbox dnt answer to the accelaration and start to make a vibration in the accelaration pedal.Help...