I have a 2006 toyota highlander hybrid 4wd with 214k miles. I recently just fixed a evap leak and I thought that would also solve the code I got for both banks running lean but it didn't. I'm going to try some MAF cleaner and hopefully, it solves the issue. It doesn't effect the drivablilty. I drove from MA to NY and back getting 23mpg which funny enough is better mpg i was getting when i drove from MA to MI back in May (before I fixed the evap leak). If simple solutions don't solve the problem I'm just going to live with it as the car is basically on its way out due to the hybrid system.
running lean means you're burning less fuel, so you will see a rise in fuel economy.
You may still have vacuum leaks.
Scotty has videos about finding those, and about code P0171 if you search his youtube channel.
