For 1000 miles your in town mileage is not that bad, but the highway mileage seems a little low. My mileage has been continually increasing as I put more miles on. I am at 7000 miles now and highway mileage has increased about 5 mpg since new. Also you may want to check TSB 08-013-04. It has the MDS reset procedure in it. This TSB has been superceded by -04A, which eliminates the portion that deals with MDS reset. There is no reason indicated why it was eliminated though, but the next to the last step calls for use of the StarScan tool to clear all DTC's. Basically though, it says:
1. You need a fairly long, open, safe, straight road for a WOT run to about 35 mph.
2. Get engine up to operating temp., engine running and car stopped put selector in "D", move it to the right until in "1".
3. Turn off all electrical accessories (except lights if needed).
4. WOT run to 4500 RPM (about 35 mph), immediately remove foot from accelerator and do not depress the brake, let the vehicle coast with the throttle closed until the vehicle speed is again at 35 mph or lower.
5. Stop vehicle and place in "Park", verify all instrument cluster warning indicators are off.
6. Cycle ignition switch "Off" and back "On", but do not immediately start engine.
7. Hook up StarScan and clear DTC's
8. MDS calibration is now complete.
If you have access to a Scan Gauge, you can clear the DTC's with that. The only cost about $125, and are well worth the investment, IMO. You could also do my MDS "On" indicator light mod. which will let you know when the MDS is active. See it at: MDS "ON" Indicator Light
Hope this helps.