[Dwayne J]

Far as the OLM I have a 2003 3.4l Impala rusting away in the yard with 235K miles I think, we bought it new and it was my wife's daily up till about a year ago. Got dealer quick lube changes at OLM most of it's life. I think the first few years she tried to have it done between 3-5K, before settling in on trusting the OLM. Car is easily the cheapest and most trouble free vehicle we have ever owned and there are no major mechanical issues with it now.

I understand that on the direct injected engines they had to change the OLM settings but generally the OLM is an adequate frequency so long as there isn't outside dirt contamination. It is pushing the limits but not exceeding.

 

[Dwayne J]

I wouldn't go 14k without UOA to confirm it is working out OK. Mobil may say 15K miles is OK but they are making a generic statement, not based on your engine, your use, your conditions.

 

[Dwayne J]

The OLM does not measure anything to do with oil quality, it is a calculation designed to account for how the vehicle is used and cold starts etc.. Back in the 90s they had it dialed in on the LT1s so that it was technically OK, those who left it go till the light came on and then tested the oil said it was spent but not to the point of harming the engine. I would expect that to be the case on the 2008 as I am fairly sure those were still port injection.
You get into the newer direct injection engines and they are harder on oil and I think GM was hesitant to increase a maintenance frequency and tried to just use the Dexos spec to keep the oil change frequency where it was.

Personally on my truck(2005 Sierra) I buy whatever synthetic is on sale with premium filter at Advance Auto and hopefully catch it at 20% life remaining, figure since it has the OLM setup for regular not synthetic I am feeding it the 20% is going above and beyond GM recommended.
My wife's 2014 Impala if I see in the OnStar email it is at 30% I tell her to make an appointment.

My current car is a 2015 SS with under 11K miles and I intend to do the third change at the dealer in the next week or so but I figure it is just getting broken in, my commute is short and this is a LS3 that will be modified one day. I don't drive it too hard but I do enjoy it.