Gearbox

I have a 2002 corolla 1500cc AT VVT-I, long story short. My gearbox siezed working and I replaced it wit a second hand one. The new bearbox does not seem to have power and it is struggling to get above 165Km/h. There are moment when accelarating that it jerks violently almost like its failing to select overdrive. Basically it goes down to third and fourth and third again. We have checked all the sensors, is there somethin that I might be missing that needs to be adjusted. Computer diagnosis does not register errors