I have an '05 too & had the same problem. 1st, the main culprit (some won't like to hear this, or believe it) is the amsoil (interceptor). I ran that the first two seasons (bought new), turned oil pump rod 2 turns, but it was always sucking it (oil) down. Always ran rich, plugs were all gunky as well as power valves. I've attached pics I have of my plugs on amsoil. I tried the cat oil and had a big improvement just from that. Just looking at the two oils, amsoil looks like water next to some others. I'm not bashing Amsoil, just doesn't seem to be the best choice for my sled. Ultimately, I switched to Citgo Sea & Snow based on opinoins here and on one trip I ran out and had to run it. My oil consumption AND performance has never been better. Plugs are a nice cardboard brown, pulled a power valve and didn't even need to clean it this year. I run it for two seasons now, 2000-3000 miles, and will continue to use it. I also added a fuel reducer, but that really only affects Wide Open Throttle. At least two seasons with that too. I have just over 5000 miles on mine and as confirmed last week, still give my buddies with Apex's & 800xp's fits, mostly on the top end, mid range is always a toss up. Running the amsoil, on avg. I would GPS about 106-109mph with oil soaked plugs. I now avg. 112-116mph on GPS with nice brown plugs. Not trying to start any my sleds faster conversation, just stating my results from some experimentation.