Check with your dealer! Has your 3.5 ltr lost 5 mpg? Check engine
light on? Does it run rough? My '06 has. I brought it to the Chevy
dealer, where I bought my Canyon, & they told me the was a "campaign"
on the engine. Well there is no "campaign", it is a service bulletin!
(this may become a campaign in the future.) These engines have bad
cylinder heads. The valve seats are too soft. Have your dealer check
it out & get it taken care of under warranty. Otherwise this is about
a $3000 repair.
Good luck.