I had the same type of problem on my 1997 Ram 1500 with the 318 engine. Did a full tune up, cap, rotor, wires, plugs, checked the routing of the wires as there was a TSB on them, etc. Same situation like yours, the light would come on for a random cylinder misfire in cyl 2 if I remember correctly. I swapped out injectors, nothing. Changed plugs out, nothing. Finally gave up and it seemed to go away with more driving I did.