Not familiar with tusk clutch kits, but the slipping problem sounds like you either have bad clutch plates or your cable is adjusted so tight clutch is always disengaged. Clutch plates at dealer for my bike run about $90, so your $35 pricetag sounds like a steal--if they are any good. As for the oil, repack the silencer and get the bike to operating temp for a while and see if problem is still there. If so, you are probably jetted too rich or sucking up transmission oil through the crank seal. Sputtering at wide open is likely jetting. Start by taking carb apart and cleaning jets and carb really well. Check float height too. Doubt the plug is your problem because it is more apt to crater at low speeds rather than high speeds.