I'm not sure you can assume it's a sensor at all. Have you checked for vacuum leaks, fuel pressure, etc?

 

 

Lean code doen't mean the engine is running Lean

Lean code means the computer is adding more fuel than it calculated so engine does NOT run lean

Lean code will usually be set if computer has to add more than 15% more fuel than calculated.

Computer uses engine RPMs, throttle position and MAF(air flow) sensor data to calculate how long to open each injector to get the 14.7:1 air:fuel ratio
After it is burned in the cylinders computer looks at O2 sensor voltage to see how much Oxygen is in the exhaust, too little oxygen is Rich, too much is Lean
If Lean Computer opens injectors 2% longer, if still lean then 4% longer, ect.........until O2 voltage shows correct oxygen levels, this takes less that 2 seconds
If above 15% then computer sets Lean code and notifies driver by turning on the CEL(check engine light)

If an engine is actually running Lean it will ping/knock on acceleration every time you press down on gas pedal.

If you get Lean codes for BOTH banks on a V6 engine then it won't be O2 sensor issue, very much of a long shot that BOTH O2 sensors start to fail at the same time
To effect Both sides of an engine it needs to be a problem common to both banks.
MAF sensor is common
Upper intake manifold Vacuum leak is common
IAC Valve is common but..........you would have high idle issues after warm up, but good to clean these

The air tube from MAF to upper intake needs to be sealed tight, leaks here bypass MAF so can cause lean codes
PCV Valve is part of that, PCV Valve is a "controlled" vacuum leak, if PCV Valve sticks open it becomes a vacuum leak

And one thing that is often over looked is Fuel Pressure, computer has no fuel pressure sensor
1999 computer will be programmed to "assume" 55psi fuel pressure, so it knows how much gasoline will flow out of an injector when it is opened if there is 55psi pressure behind it
1998 and up Rangers used 55psi
If there was only 30psi then less fuel will flow in so computer has to open injectors longer and........................yup, lean codes on both banks

MAF sensor is monitored, they can get dirty but if they fail you usually get a code for that, but not always
Vacuum leak is by far the most common cause of Lean codes

After engine is warmed up, let it idle
Unplug the 2 wire connector on IAC Valve, it will close all the way
Idle should drop down to 500rpms or engine may even stall, either is GOOD, it means no vacuum leaks
If idle stays high then there is a leak

If idle drops down then check fuel pressure

 

 

Only the FFV 3.0. Non FFV 3.0's and all other engines were 65psi.