The only GMC to be offered with a four-cylinder engine, the Terrain crossover is not surprisingly, the best GMC for gas mileage.
That's true if it's ordered with the base 2.4-liter four-cylinder engine, at least. Available in any trim level of the Terrain--from SLE to Denali--the four-cylinder is designed with all kinds of fuel-saving technologies that stretch its highway mileage to more than 30 mpg. Among those features: direct injection, and an 'Eco' button which, when engaged, causes accessories like the air conditioning compressor to be a little more conservative, has the torque converter lock up a little earlier, and makes the transmission a little more reluctant to downshift.
The net result is a crossover that's at least part miser, especially in its size class. The four-cylinder Terrain earns an EPA-estimated 22/32 mpg, a figure better than all the other mid-size crossovers except its corporate cousin, the Chevy Equinox. Adding the Terrain's available all-wheel-drive system doesn't ding fuel economy too badly: it still is rated at 20/29 mpg.
Once you choose the Terrain's optional V-6, the numbers take a big fall. The 3.6-liter V-6 makes much more power, but that leads to gas mileage estimated at 17/24 mpg--or even 16/23 mpg when all-wheel drive is fitted. Those figures are more in line with the seven-seat Acadia crossover--not a surprise, since the drivetrains have so much in common.