I picked up my '06 with about 170k on the engine in January and I only use it on weekends. About ready for my first oil change. Records indicate previous owner was using conventional oil. I have a 2002 Land Rover Discovery II with 180k that LOVES Rotella 15w 40 (T5). Thoughts on Rotella for our 5.3's, Summer Texas heat coming, and we plan to drive from Dallas to Panama City Beach in a few weeks. Also, which Rotella? T5 or T6 or other?