Dark wet gunk on fresh plugs is a little worrisome, but it could be gas-soaked carbon. If they smell strongly of gas, you may have a leaky injector or cold start injector, so then pull the rail and cold start injector and put into bottles and run the pump to see if you got leaks. There should be no or <1 per each couple of seconds dripping. You can check spray as well with ignition on and open the throttle, clicking the throttle switch.
If bad running warm, likely cause is coolant temp sensor at front of head or connection thereto. Cold engine needs rich mix. I can't recall if disconnecting that wire makes it rich or lean.
If not gas, rings.