While driving seventy MPH engine hesitates

Car drives like a dream but I am having some issues with the car when I am driving 70 miles an hour it makes a hard hesitation like quite loud and I release the gas pedal because it sound likes it going to break down. I come to a stop light 25 miles an hour and when I get ready to step on the gas it makes the same noise and I am stepping all the way down and it doesn't want to go. I took it to a transmission place and had the transmission looked at and the mechanic said transmission is good. I have had tune up on car and manifold has been fixed on it, sometimes the tachometer doesn't always work. It's very difficult to explain the noise that I hear.