3rd Gen 4Runner low on power (5VZ)

I am helping a friend with her 3rd gen 4Runner with a 5VZ and automatic.
It's low on power, and reporting a lean condition.

They get a check engine light that comes and goes, and when we pull codes we are seeing a Lean condition in one bank.

I haven't worked on it yet, but I am preempting the work I am going to do this evening.
So far as I know it has had:
1. Downstream 02 Sensor replaced.
2. MAF Sensor replaced.
3. Ran a can of Chevron fuel injector cleaner through the tank.

My Plan of Action is to:

• Pull the code to get the exact Error(s).
• Test the upstream O2 sensor (AFR sensor, IIRC).
• Pull the spark plugs and check the condition.
• Compression check the motor.

Any other things I should check or am I just spinning in circles without pulling the codes?

 

I would def start with pulling the codes. Has she been the only owner?