Oh, one more thought. I had an issue with my prior '93 SHO fuel economy which took a nose dive over a few weeks, even though it ran fine. That suggested to me it was running rich. I remembered this started shortly after cleaning and re-oiling my K&N air filter. I took out the MAF sensor and noticed the elements were a dull gray. I used electrical parts cleaner (before I knew CRC sells a MAF sensor cleaner) and cleaned the sensor. The elements now had a shiny chrome appearance and my fuel economy returned to normal.
You might want to clean your MAF sensor.
-Rod