I would check into changing the starter solenoid asap. You will probably find 1 really worn spot on the flexplate.V6 engines stop in 1 of three places. The milling you here every couple of days will appear in the same spot.Since it is expensive to change the flexplate...I would start with the starter.
PS...you will find a starter engagement point every 120 degrees of rotation of the flexplate.
Good luck.
