Synthetic Oil Switch?

Nope, there is no reason at all.

 

I think most owners like to do things to better their Tacomas. This is one simple thing you can do. It is definitely not required, as Toyota engines in general are very easy on oil.

 

I ran it for 20,000 miles in my sport bike. That oil sheers down really quick, I wouldn't use it for extended drain intervals.

 

I've had my used Rotella analyzed. Lab stated that it still was over 75% effective, after 15K miles. Do you have a lab report, or just an anecdote?

 

What does 75% effective meen? 75% life remaining? By that logic, go for 60K!

Its a tough oil which resists contamination and has a high TBN however it sheers down quick. Nobody recommends T6 for extended drain intervals 10K+ but if its working for you go for it.

 

You are thinking linear, the 75 % effective could go down to 60% in a matter of weeks, or a few hundred miles, and why would I want to risk that? In other words, the oil was still effective at 15K miles of use, which is a lot more quantifiable than your anecdote.