MPG, injectors, O2

[Qdog]

My mpg has dropped from 17-18 to 16-16.5 for my normal driving. This after a full plenum/throttle body/fuel rail cleaning and bench cleaning of all injectors. The injectors went from 70-75% of rated flow rate before cleaning to 100% after. I was expecting a mpg improvement, not a drop. I'm thinking it must be my original O2 sensors (hi miles). If they failed to trim a lean condition due to low flow, they are failing to trim a richer mixture now. Is this logic valid, or is there another cause I might have overlooked ? I cleaned the IAC and it seems to be working well. New plugs went in too, and the old ones looked good, neither burned or fouled. They were the hotter heat range of the 3 NGK options for the Q. The new plugs are the standard range, middle of the 3.

[PalmerWMD]

O2 sensors are good suspects.

Fred..