Back when we were kids we'd mess with people by pouring diesel fuel into their tanks. It makes the vehicle difficult to start, it'll run like a dog and have hardly any power. Ask your mechanic to check and see if perhaps maybe you got a bad tank of gas, maybe watered down, contaminated, or otherwise. No computer will tell you what type or grade of fuel is being burned, and even if everything is functioning properly the vehicle won't run properly if the gas is bad.