If you really want to know what the oil like after use you should do an oil sample. If you are really concerned you can do a sample of a brand new bottle of oil then do a couple used samples so you get a baseline and that should help determine if you need to switch oil or if it is in fact still good to go.
We use fabco / cat oil sample kits as they only cost $12 and that includes the postage.
As far as oil goes we use at my work off road oil mainly marketed for farm tractor use. With 7000 miles on my duramax our oil rep said the #'s on the sample would have to triple before he would even start to worry so this oil change is scheduled for 10k miles and I will recheck then to see where we are at.
The oil we use is called Central Petroleum Company (CenPeCo), I have personally looked at the bearings on a 200k mile lumina 3.1l engine that looked like they were just installed they looked that great.
If you would like lots of info I can give you our oil reps # and he will talk your ear off
he knows his product and has proof through oil samples that it works!
Good luck and send me an email if you want to talk more
