make sure the firing order is not off by one or more plugs .. drivers side front to back is cyls 1,3,5,7 .pass side front to back is 2,4,6, 8 firing order for all mopar V-8's is 18436572 distributor rotation is clockwise ...
check the cap and rotor, as well as the plug wires. You could also try running some seafoam through it. If your still getting the misfire try swapping #8 injector with one form another cylinder and see if the misfire follows it
It could be the wires (did you replace plug wires with the new plugs)?
A compression or leakdown test would be next if all the above fails to find it.
just on #8? does it have oil on the plug? have you changed the plenum gasket?
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