99.9% will tell you the 4.0. It is an incredibly reliable engine that will last forever. The only reason I bought my 2011 was because getting a low mileage 2006 would have only cost me about 3k less because Jeeps hold their resale value. I live in a military town so all the dealers figure if I don't buy it for that price someone else will. If you can find an 06 for a price you are happy with do it.