How did MPG go up 2 mpg on new 535i plus GT

I just saw that the 2011 535i is rated at 20/30 mpg combined 24 just last week it had 19/28 combined 22. This is the same for the 2011 535i GT vs the 2010 535i GT. This seems like a significant difference and it must have come with cars built starting in Sept because that is when the GT went from 2010 to 2011. Wonder what they did to get this increase. I don't see any explaination ion the BMW web site.

Not sure of this helps much, but the follow two snippets are from the July 9th BMW Bulletin # B-1-0710-11-All. This may give you some direction or insight.

Gas Guzzler Tax Currently there is no Gas Guzzler tax for any Model Year 2011 5 Series Gran Turismo model. This eliminates the Gas Guzzler tax on vehicles that have been wholesaled after June 24, 2010.

5 Series Gran Turismo (Model Year 2010)
Gas Guzzler Tax
As a result of final confirmatory fuel economy testing, the highway and combined values for the 550i Gran Turismo have been increased by one MPG. This eliminates the gas guzzler tax on vehicles with a Monroney label dated after 6/24/2010.

5 Series Gran Turismo (Model Year 2011)
535i xDrive
Model Year 2011 for the 5 Series Gran Turismo starts with September production. With that brings the addition of a new model, the 535i xDrive at a base price of $58,300 completing the 5 Series Gran Turismo product offering. The equipment profile is the same as the 535i rear wheel drive model however Integral Active Steering (2VH) is not available.

I saw this report concerning the 550iGT but nothing on either the 535i 2011 Sept prod or the 535i GT 2011. When they get a significant increase in Gas Mileage like this is the engine re-tuned some way? Is this a mechanical switch of the Engine computer? or a software change for the existing one.

The reason I ask is I had a 535i GT produced Aug 14th so It is a 2010 model. 2011 production started Aug 30th. I certainly would like the combined 2 mpg increase in mileage on my car. If it is a software mod. then how would I get it applied to my car? It just reached the Port of Brunswick returning from a ED. It still needs to go thru the VPC there-maybe they can and will do it. or am I to optimistic?