oz rally 2002 hiccup?? Help!

Hi all    I have a 2002 lancer oz rally with the 2.0l engine and 5spd tranny. I recently developed a hiccup in the car. When I shift from 1 to 2nd and goto exelerate it hiccups 2 times and then goes. It also happens in third and forth but only under load. I replaced the spark plugs but did not solve the problem. I am stuck as to what the problem is but do not want to just start putting parts on it. It gets a little costly after a while. It is intermitant only does it sometimes. The car idles fine and runs well at higher rpms but if you slow down a bit and go to exelerate agin it will hiccup !  Any ideas or anybody have this happen to them ?
 
Thanks any help would be apperciated.

Did you check the park plug when you changed them.
checked for aggressive burn on the spark plug.
Check the fuel line,spark plug wires, etc etc