Just my 2 cents, check your air cleaner. Bought my truck and did not check it before buying it (yes i know very stupid of me), drove it home and got horrible mileage. Scared me really bad haha. Opened up the air box to find out that the PO put to much oil in the engine. VC has a plow off rose that runs to the air box. My air filter looked like a sponge. Changed it, cleaned the throttle body, and C-foamed the engine, getting good mileage now.