My 2005 XC 700 the dec light will flash when you really hammer on it, But it only will do it 1 out of 25 times you really get on it. I have premium gas in it and it is fresh. Cleaned the exhaust valves. I did switch the plugs from factory champion to ngk BPR 9 es this is what the dealer told me to run. Could it be the plugs? Or what do you people think?