throw cyl 1, 2,3 and 4 cyl misfire. when im in 5th gear cruising at low rpms it stuters, but if im in the higher rpm runs and pulls fine....any help appreciated

already did full tune up...plugs wires,cap and rotor.

 

is it every time or only every once and a while? are you sure its rpm related and not throttle position related? got any spare igniters you can try?