Waja exhaust question

[noobiejlcs]

i realize that b4 i change my waja 1.6 auto trans bullet and muffler , the pick up is not that powerfull , but after i have change it , i also feel that when my car lost its power at about 120km onwards , its kinda hard to speed up to 160km , so i juust wana ask is there anything i could do to increase the pickup and still have power when at high speed ? Thanks ....