Lean condition??

So have you tried it with 91 octane yet, OP? From Chevron, Shell, or Exxon.

Cheap gas from cheap stations, I.E. most grocery store gas stations, have caused so many problems for vehicles, that some including Jaguar have stated that your warranty will be voided if you purchase gasoline from said places. Costco's, Wal-Mart's Murphy stations, etc...Clogs filters, burns up pump motors, causes corrosion in engine components.

You have almost a $30k vehicle. Give it the good stuff.