I've a 2010 LT Cobalt and live in Portland, OR area. I had to change the oil every 3000 3x in a row to eliminate sludge...it worked. If I recall my dealer said to switch to 5000 mi intervals after I completed the 3 3000's. Does 5000 sound adequate? If I stretched the 1st one to 6000 would that be okay? That would put the next interval's mileage at 110,000 vs. 109,000. Much easier to keep track on the multiple of 5. Thank you. Update: Called dealer & they said every 3k miles. Does that sound best or would 4 or 5k be better? Thanks.