Might be worth checking the the rubber insulators between the two manifold pieces. You can see them right below the injectors. I had a #3 misfire. Easy way to check them is with water, you will hear the difference when the water hits the spot. Low water flow and one insulator at a time. Another way if the water doesn't work is with engine cleaner or starting fluid (flammable- be careful). I found mine with water, then used starting fluid to confirm the spot, and again to confirm the repair.
Bought the rubber from the local Goodyear Rubber dealer, got them and had them installed the same day. 2" ID if I remember, 12 inch length is all you will need.