My X5 4.4 has been sounding a bit 'lumpy' the last few days, power seemed a bit lazy...Turns out that all the spark plugs need to be replaced...they were not firing properly...The car was only in the dealer for it's first service (24k) in January 2006, so I'm not too impressed with them.....I'm using 98RON unleaded...could it be that this is causing the premature wear on the sparkplugs?