The most significant development is a new engine. Instead of the V-6 or V-8 found in Ford's Explorer and Mountaineer SUVs, GM opted for an all-new in-line six-cylinder. Many of us grew up around straight sixes. Chevy trucks used a reliable straight six in the old days, and Jeep has long used a basic straight six in the Cherokee. An in-line engine is, in fact, inherently smoother, simpler, more durable, and more fuel-efficient than a V-6. But the in-line configuration is also longer and, until recently, has been stuck in a cast-iron shell. Advancements in electronics, metallurgy, and manufacturing methods, however, have enabled GM to make this proven design sing a new high-tech song.