Drove to VT this weekend. after 2 hrs of driving with cruise on set to 70mph I start feeling the car jerking when it is climbing hill. Not a shudder but sharp jerks. Mpg drops like a rock. Took it off cruise and pressed hard on the accelerator and same issue. Jerked snd stuttered then would go. We had just fueled up so my guess was bad gas. Stopped, filled with high test and added fuel additive. Mpg went up and no issues for the next hour or while driving around town. Ride home now, after about the same miles and time driven, the issue reoccurs. This time I pressed on and did not stop. Except for a refuel stop again with high test early in the trip back. Mpg dropped. Tach would spool up and then go. Much worse with cruise on. With cruise on it was not as bad and I got mpg to go up but no where near normal. This trip the car usually gets almost 26mpg. This weekend I got 20mpg. Any ideas?