My DD is a 2001 Suburban with the 5.3 engine. I've got about 195,000 miles on it and it runs pretty good but I'm wondering about changing the grade/type of oil that I'm using to help it live a little longer. I've been using the manufactures spec 5/30 conventional but I am thinking about something a little heavier or maybe even a synthetic. It burns a quart every 1000 miles or so and it rattles like a diesel (piston slap) for a couple of minutes after cold starting but only when the temp dips to 40 or so. Any suggestions?