Here are a few setup things to try.
Make sure the track is aligned and that the skis are toed out no more than 1/4". Check the carbides, too. If they are bent, that will add friction and cost you mileage.
Check all the bogey wheels to make sure the bearings are all ok. Some guys will replace the bearing grease with synthetic grease because it has less friction, less friction will give you better mileage.
Make sure the clutches are clean and the offset and deflection is set to spec. Any belt scrubbing can really eat away power, which also kills your fuel mileage.
What kind of chaincase fluid are you using? Synthetic chaincase fluid is less viscous and will cause less resistance to the sprockets and chain, giving you a bit more power.
None of these things will be a magic bullet to get you great fuel milage, but if you do 'em all, you could gain 1-2 mpg at very little cost. It's worth a try.
Check the fuel pressure. As the Cat fuel pump gets older, it seems to develop greater fuel pressure. If the EFI is being overpressurized, it could give you a rich mixture and contribute to lousy gas mileage.
More options
Replace the sliders with the super slippery ones, those give less resistance to the track.
Port the track, there are weight savings in the rubber you remove and less rolling resistance in the track.
Add a lightweight pipe/silencer. Those are a bit spendy, but can give you more power, less weight, and sometimes better mpg. With the pipe/can option, you may have to upgrade the ECU and clutch springs/weights/helix to get the maximum out of the engine.
Lots of things to try, some inexpensive, some more expensive. Let your wallet be your guide
