I recently bought a 06 GMC with a 5.3l engine. It has about 290000km(180000m) on it. I did an oil change immediately with standard Penzoil, but since it was pretty black I decided to do another fairly soon. I've put about 2500km on it now, so I'd like to do it now. I'm trying to decide what oil to use. It has a slight tick sometimes at start up, which may be the engine or possibly exhaust leak. Doesn't seem to burn oil, but does leak from the cooler block plate, not unusual for these. I usually use PP or M1,depending whats on sale, but I'm considering using a high mileage in this one. It doesn't tow often, but will tow a trailer and quad on occasion. Being in northern Canada, we don't necessarily have all the options others do, but do have most of the usuals. Should I run the usual synthetics or a high mileage? One concern is that I will be running synthetic in winter as it gets very cold here, considering a 0W-30. What would you do?