I purchased an 01 Tahoe this summer, which currently has 70k on it. I will be doing my 1st oil change in the upcoming month. I am currently about 3k into this interval, and my oil level has not moved at all. I am unsure what the PO used, but was assured that they stuck to strict 3k intervals. I was set to run PYB for about 5500-6k for the near future (it is a low use vehicle, no towing, and mostly highway miles). With the Menards sale of QSUD, I am re-thinking the process. My concern, though, is going full synthetic at this juncture. Not because of a misconception of synthetics causing leaks, but unsure what is behind the gaskets in a 14 year old engine and the effects of increased cleaning. One thought was to run a 'frankenbrew' of 3 quarts QSUD and 3 quarts PYB. What are your thoughts regarding this upcoming oil change?