Ok well i have a 98 ram, 5.9 4x4, i redid the plugs, wires, cap and rotor, and it ran good for a while, recently it started to slightly missfire at like a red light every couple seconds, with no check engine light

now it has started to missfire badly, throwing a code and running really bad like bucking and what not

I checked the TSB about the routing of the wires, and i did that, the code im getting is a cylinder 4 5 and 7 misfire

What else could it be? how can i go about diagnosing a misfire?