I just hate to beat a topic to death but I am out of options. I tried everything I could before asking for advice.
Fuel mileage dropped from 38-42 to 27-32 mpg. The mpg was verified over 10 tanks using GPS.
In the effort to regain fuel mileage I performed maintenance.
Replaced spark plugs
Cleaned air filter (K&N)
Synched the throttle bodies
Checked the TPS
Replaced fuel filter
Adjusted the secondary throttle plates.
Checked tire pressure
Rear sprocket carrier bushings are tight.
Clean and adjusted the chain (16 tooth front sprocket, Stock rear) (Fuel mileage did not go down when I changed to 16 tooth sprocket 10k miles ago)
The bike runs great. Plenty of power and no hick-ups.
2003 DL1000
44k miles