John,
In my Jeep I have been using Rotella 10W30 as it is formulated for diesels and still has some of the additives to keep the cam & lifters lubricated. However, I just learned a couple of days ago that "they" say not to use it long term as it lacks the detergents, and tends to sludge more - can't win.

I have never gone with full synthetic, as I can't get comfortable with the extended change intervals and the cost is prohibitive at 3000 miles!! In my wife's Grand Cherokee I use MotorCraft's syn blend, as it calls for a 5W20 and there are not too many out there. I have read that some of the syn blends have very little synthetic, and in the past I have mixed my own using about 25% full synthetic staying in a common brand.

There is a web site, Bob Is The Oil Guy, http://www.bobistheoilguy.com/, where you can spend hours learning more about oil formulation than the average mind can digest.