09 Acadia, 125,000 miles. For the past year I MUST change the oil faithfully at 5000 miles, or my car starts missing really bad. Nobody believes me, but the minute I change my oil, the miss disappears, only to reappear at about 4500 miles into an oil change. What the heck is going on? This has been happening for at least a year. Otherwise, the car runs great. I'm not talking about a little hiccup, I'm talking about a major jerk miss. Using full synthetic oil. Any suggestions?