I have been checking the posts and found some similar problems but never found any results. 1999 1500 with 318 engine. When you first start the engine it will have a miss in it. Only does this if it has been sitting for several hours. Sometimes engine light comes on, sometimes it doesn't. Each time I have had it checked it points to #5 cylinder misfire. Will continue to miss even when you drive it, not just at idle and then goes away after about 30 seconds. I have changed wires, plugs, cap, and rotor. Tried to run some injector cleaner through it, but doubt that is the problem since it does go away. Fuel pressure isn't the problem, I have waited for the fuel pump to shut off, same issue. Intake and plenum gaskets recently replaced, and again, goes away after a short time so doubt that is it. Brand new battery too. My thoughts, possibly a lifter collapsing??

 

I'd swap the #5 injector first, then see if the misfire follows it...if not, either a defective plug or wire, or internal issue.