Bank 2
V6 engine has 3 cylinders on each "bank"
Bank 1 is passenger side
Bank 2 is drivers side
Only getting Bank 2 Lean code is more likely to be lower intake manifold vacuum leak, bad spark plug or injector on that bank, or O2 sensor on that bank
Low fuel pressure would cause code on Bank 1 and bank 2, same for upper intake vacuum leak or faulty MAF
These effect both banks
Bank 2 is not "running" Lean, thats not what the code means, Lean, or Rich, code means computers fuel calculations are off.
The computer calculates the amount of fuel needed on each Bank by the air flowing into the engine, it then opens the injectors to add that amount of fuel, after the fuel is burned the O2 sensor reads the Oxygen levels in the exhaust on that bank, if oxygen level is low the exhaust is Rich, if oxygen level is high the exhaust is Lean.
If Lean computer opens injectors longer on that bank, until O2 reports normal oxygen levels
If computer needs to add 15-20% more fuel than calculated it will set a Lean code for that bank, if 15-20% less fuel then Rich code.
This all happens in less that 2 seconds so engine is never actually running Lean or Rich.
Your thermostat may be going bad, it is not opening as it should so engine is overheating until it finally opens.
Replace it, they are not expensive