dnewton3,
Thank you for your comments. To answer some of your questions and address your comments:
This vehicle has only seen Mobil 1 EP its entire life, since factory fill was drained. All UOA intervals reflected Mobil 1 5W-30 EP/SM, except the last two, which were SN rated.
Right now, my plan is to move to an interval of 7,500 or six months, whichever comes first. Right now, I have three vehicles in my family's "fleet" and will be adding a fourth in a couple of months. I am very busy with family/career, and want to reduce the number of oil changes I do - I'd like to limit it to 2 oil changes per year per vehicle, if I can. Both Tundras I own (the 2006 that is the subject of this series of UOAs) and the 2011 specify 5,000 mile oil change intervals. But the 2006 is now about to be out of [extended] warranty. The 2011 has a 125K warranty on it.
I'm considering a new 4 cylinder Camry as the fourth vehicle - not sure if I can afford it. But if I can, that vehicle specifies 10,000 mile/one year oil change intervals. If I acquire this vehicle, I'm tempted to use Amsoil 0W-20 in it as I do like that oil's additive package and I think it would perform better than Mobil 1 EP on an interval that long.
My son will become the principle driver of the 2006 Tundra, but as he still lives with us (as a college student) the vehicle will still be sitting in my driveway. His driving style, however, is as you would expect of an 18-year old - a bit aggressive.
Regarding keeping the data stream going: I've often thought about this. One approach is to continue the same UOA monitoring, but choose a different oil, and compare it with the Mobil 1 EP. Another thought, and one that I am leaning towards: Trying to understand how engine wear changes (at least according to UOAs) as the vehicle ages. I've often wondered why "High Mileage" oils have heavier amounts of anti-wear additives in them. Apparently, engines wear more as they age. This seems counterintuitive to me, so it would be interesting to see how the wear metals trend as the engine goes well past 100K miles.
With four vehicles to maintain, I can't afford to perform UOAs on all four. I've pretty much stopped doing UOAs on my 2003 Lexus GS430. Perhaps my son will be willing to fund UOAs on the 2006 Tundra. He has seemed interested in the reports I have been doing, we'll see if he is interested enough to pay for them