Houston, we have (another) problem...

There is no specific sensor that triggers lean codes, they typically are set when total trim exeeds about 20-25%.

I don't have time to explain it in detail at the moment but I'll leave a video class by Paul Danner about fuel trims, just be aware that Toyota AFR sensors operate differently and at different voltages than the standard O2 sensors he is explaining but the principles are the same.

https://youtu.be/oRX2V6_a3dc

 

So I got my Fuel Pressure test kit from Amazon for $32.
It has the Banjo-bolt adapter that I see in my Haynes manual.
Is there another way to test the fuel pressure on a 3.4L V6 with the kit below?

Most other cars have a handy Schrader valve somewhere. I was just thinking it would be easier than messing with the front of the fuel rails.