1993 Saturn Wagon SPUTTERS/REVERSE PROBLEM

I HAVE A 1993 SATURN WAGON, APPROX 125K MILES. RECENTLY I TOOK THE CAR AND REPLACED THE BATTERY AND THE ALTERNATOR. THE DAY AFTER I PICKED IT UP THE CAR BEGAN SPUTTERING ANYTIME I DRIVE OVER 40 MPH. THE CAR WILL ALSO SHUT OFF WHEN I TRY TO PUT IT IN REVERSE TO BACK UP. THE CAR DOES NOT DO THIS ALL THE TIME SOMETIMES IT RUNS SMOOTH. I KNOW A TUNE UP IS NEEDED BUT WHAT WOULD CAUSE THE CAR TO SHUT OFF WHEN SHIFTING IN REVERSE? THANKS[/b]