99' prism runs rough and cant go up hills

i have a 99 prism and a few weeks ago it started sputering, so i changed the wires and plugs, still not working. so i got a code for a misfire on 2 and 4 i think it was. so i replaced the coil pack and it ran great for a day. now it is doing it again. if the pedal is pushed in to far it starts to sputer and if your going up a hill without speed i might make it, but going 5mph. kinda runs better when going above 35 or 40. any help please????