I have a 2004 toyota allex. under hard acceleration the revs get stuck for a while and the speed goes down for a while but gradually picks up speed slower than when the accelerator pedal is preesed halfway. Before the car could reach 180km/h but now it can only go to 130km/h. What could be the problem?

many things can do that, but often a bad fuel pump or clogged fuel filter, pressure test them first