When you did all the work on the car, did you happen to disconnect any fuel injectors? It's pretty common for the injector clips to break after years of engine heat, etc., and an injector that is not working could cause a lean code. Although I'd expect it to also set a code for a specific cylinder misfire.
With the lean bank 2 code (assuming that's what it said since you mention "left") a vacuum leak that would effect just that bank does seem more likely.
Would you mind sharing the exact diagnostic code number?
-Rod