poor diesel mileage on 2010 Volkswagen Jetta TDI

2010 tdi jetta 13000 miles when i bought it last month. kept in garage. seller said he got 45 mpg . car was used very little. I get 30 to 35 miles pr gallon. every body I talk to gets 45 to 50 miles per gallon even 10 year old vw diesels. vw dealership says everything checks out ok. at 70 miles per hour , tach is at 2400rpms.

1 answer
Simple stuff would be air filter restricted. Very low tires?
6 speed transmission or automatic DSG?
No check engine light (MIL)? Most causes would also turn on the check engine light.