misfiring/loss of power when driving my 03 fiesta 1.3 lx?

my fiesta 03 1.3 lx when driving miss fires and there is a loss of power and accellaration. the car seems to idel fine but miss fires only when driving and seems to not pull away. the engine light came on but then i changed the leads and plugs it went away and came back a day later so i changed the coil pack and the light went off. now few days later it started to lose power and miss fires you have to rev high in low gears and gradually accellarate if you apply to much preasure on the accelarator then it starts to stutter so i used a complete fuel system cleaner 500ml and its still missfires with out the management light coming on. so i took the plugs out and cleaned the leads and plugs and put some bonding gel in the leads then connected them up and it went away but comes back real slow but comes back to stuttering when driving. anyone have any ideas? pls share.