i hit gas pedal then stalled

Car was tapping when i hit gas pedal then stalled and wouldnt start next day was tapping VERY loud, then stopped!! now car is running great??2 of my mechanics are stumped please help!? i have a police 2001 vic i maintained it well. i had got some gas on this day, and drove to work all was fine, then when i was driving home, i drove about 15minutes on the turnpike about 65-70mph. the engine was tapping when i hit the gas, pretty loud and fast tapping i was at about 65 mph, i pulled over immediatly, and when i was in the shoulder slowing down the car stalled and wouldnt start again..

the next day my mechanic said it started but was tapping or knocking sooooooo VERY loud he was unsure if he was gonna make it across the street, cause it was very loud.. then he started it again and it was fine, then started it again and the very loud tapping or knocking was there again, this happened a couple times.. now i took the car back its been 3 weeks and it been running so good and quiet in the city????????? they have no clue what happened? i almost got rid of the car to a junk yard for soooooo little money!!!!!! cause we thought the engine seized. it obviosly didnt...???? BAD GAS ?? IS MY GUESS FROM OTHER PEOPLES SIMILIAR
PROBLEMS? someone with knowledge please help me i dont know what to do. OH we had problems with this particular gas before.. sorry its a little long....