Gas mileage isn't usually the strong suit of pickup trucks, but the mid-size segment still has a few four-cylinder offerings left in it. Unfortunately, with the big improvements in fuel economy in the full-sizers, those smaller trucks still aren't much better at sipping gas.
The Toyota Tacoma is a good example. It's still available with a four-cylinder engine in its base model. The ratings for that standard two-wheel-drive, four-cylinder truck peg it at up to 21 miles per gallon city, 25 miles per gallon highway. Not bad, you say? The V-6 version of the latest Ram 1500, with an eight-speed automatic and a lot more room, is rated at 17/25 mpg. The Tacoma, with the V-6, drops to 17/21 mpg, or as low as 16/19 mpg when four-wheel drive is ordered.
It's worth considering, as well, that if you're planning to push the four-cylinder model to its limits, your mileage won't be any better in the real-world (perhaps lower) than that of V-6 models. But if it's mostly light commuting you do, you may find better mileage than in the Ram, or Ford's 23-mpg-highway F-150, or even in GM's full-size hybrids—the Chevrolet Silverado Hybrid and GMC Sierra Hybrid.