I am hoping to get some real expert advice / recommendation for the right oil for my applications. First, I live in Texas – it is hot here. Vehicles are 05 3.9L V8 Thunderbird with less than 3k miles, 04 5.3L V8 GMC Envoy with 15K miles, and 95 3.5L V6 Chrysler Concord with 84K miles. Typically these vehicles are driven in a stop-and-go environment. I am not a wealthy man but I do not mind spending a few extra bucks to get the best oil for my vehicles, well maybe the Concord does not need the best. The problem is identifying the best. As others have experienced, Mobil, Amsoil, Red Line, Royal Purple, all say they are the best but when you push to get data to support the claim only a “party line” is provided and these brands tend to not want to compare themselves to the others mentioned except to say that they are better. Better? Why? That is my question. Currently I use Mobil 1 5W20 in the Thunderbird, Mobil 1 Extended Performance 10w30 in the GMC, and Mobil 7500 10W30 in the Chrysler. Extended OCIs are not my objective, using the best oil is. I have compared the numbers provided by Mobil, Amsoil, RL, and RP and none are clearly best based on those, at least not in my opinion. Additionally, I do not know what some of the numbers mean like is HTHS = 3.8 good or terrible? I am thinking about using Schaeffers 7000 10W30 in the Chrysler but that might not be any better than Mobil 7500. I was thinking about using Amsoil S2000 in the Thunderbird and GMC but, according to the website S2000 is not rated SM nor GF-4 and naturally the Ford suggest 5W20 and not xW30. The Thunderbird is a high revving engine so the 5W20 in Texas kind of scares me. I believe (but not positive) that the Jag 4.0 is basically the same engine as the Thunderbird 3.9 but Jag recommends 10W30 for the 4.0. So, for these vehicles, what is best and why do you say that? And, opinions on using xW30 in the Thunderbird. My appreciation in advance for comments.