I got a 03 z71 4x4 1500

The check engine light is flashing it
idles rough an when you try to give it
gas it kinda spits an sputters. Mash it
to the floor it'll get up an go till it
shifts out then goes back to crap,
once you smash on it it'll back fire in
the breather box. Hooked it up on
the computer it says cylinder 1
misfire so I changed spark plugs,
wires, fuel filter, coil packs, throttle
position sensor, pedal position
sensor an the vent valve put to
breather hose an air filter, an still
does the same thang...