Did you clear the trouble code with a code scanner after replacing the parts? Those codes do not go away by themselves; often not even if the problem is fixed.
If the cylinder is actually still misfiring; it could be caused by a sticking EGR valve, or a vacuum leak in the intake manifold (such as the brake booster hose or the hose to the transmission modulator having come loose) or by a low compression cylinder.
It is also possible that the wires were installed in the wrong order. This motor's firing order is 1-8-4-3-6-5-7-2. Cylinders 5 and 7 (the 2 cylinders closest to the firewall on the driver's side bank) fire consecutively; and they are next to each other in the cap. It is very easy to switch those 2 wires.
You also might have a sticky valve in that cylinder. Buy a large size bottle of Chevron Techron fuel system and combustion chamber cleaner, and add the whole contents to the gas tank just before filling it up. It usually takes 50-75 miles of driving for this unique formula to clean out engine deposits.