Hovercraft. What makes human build hovercraft relatively inefficient is loss of air from cushion. Most hovercrafts have "skirt" that helps to keep air under vehicle but it is not perfect.
An animal can make near perfect skirt that would adapt to earth
irregularities. Think how you put your feet on forest track. You don't need to look straight at your feet - you look ahead and remember shape of land and put you feet accordingly. An animal that looks like skate(ray) can look ahead and move accordingly to terrain, "clinging" to it. It would inhale through mouth and exhale air through holes below body, creating hovercraft-like cushion. And it would push off the ground with legs(cushion just eliminates friction, it does not propel).
100 kg hovercraft spends around 10 liters of gas per hour. I would guess that animal with near perfect skirt could easily use 5-10 times less energy. 1 liter of fuel = about 30 MJ of heat energy = 7.5 MJ of mechanical energy with 25% efficiency(goes for both internal combustion engine and animal efficiency) = 2 KWt power for our 100 kg animal. A mute swan weights 10 kg and uses about 200 Wt(about 50 km/h in migration if you take out wind speed). So our hovercraft animal would have metabolism of a bird, but it would move twice as fast.
Animal like this would be ridiculously fast - it would go on cheetah burst speed(100-120km, about 15 seconds) for hours. It would be stopped by high grass or brush, and it would have very bad maneuverability, because air cushion, unlike wheels, does not provide traction.
Evolution of such animal would be a little tricky - nature acts gradually so we need to show that small changes are beneficial. I would imagine a walking bird predator on swamps, one that attacks from ambushes and pursues victim for some ten meters. It is walking because niche of flying predators is taken by other species and though walking bird is slower, it is heavier and has less fragile constitution so it has its own niche and it would not return to flight. Legs sink in mud during a dash like this. It would lower its rudimentary wings in the water sometimes and they would create lifting force, lessening load on legs. If it exhales air under wings, then its bubbles act like grease. Respiratory system of birds is quite different from ours, separate exhaling hole could simplify it, lets suppose that our creature already had this improvement before it moved to swamps. Then exhaling hole maxes air greasing much simpler - you don't need to move your head up and down to in/exhale.
Now natural selection favors animals that can exhale more than needed for breathing. Air acts less than greasing and more as cushion now. It learns how to save air from cushion, moving wings to cover all gaps. Now it has superior way of movement for swamps - it is not hindered by mud and requires less energy than flying. As it perfects it's air cushion, it starts doing raids out of swaps to plains. There abundance of food allows it to increase size(it increases efficiency of the cushion as well). A new top predator appears...
Hunting episode. "A herd has gathered into tight mass. Even biggest and strongest bulls are afraid - a several skate-like shades slide around so fast that eyes can hardly track them. A calf comes out of bushes and hurries back to his mother. A shadow goes straight for him. He jumps to the side at the last moment and toothed jaw snaps some centimeters to the side - no matter how predator strained his legs and neck he could not make turn sharp enough at 150 km/h!
An old bull comes out to challenge monsters. He puts his horns out and shadows turn to the side. But he misses one and it passes right behind him. Predator kicks with one leg to turn his back to the bull and reaches out with other leg, grabbing bull's leg with his claws. A powerful strike, aided by a hundred kilograms of predator weight, passing at breathtaking speed of 50 meters per second, easily breaks thick bone. With loud bellow bull falls to the ground. His fate is sealed..."