I read the topic and saw this touched on already but I'll talk about it further:
If you're into customizing, You can go get one of the G.M 1991-1996 Whale Wagons (Buick Roadmaster, Chevrolet Caprice and Oldsmobile Custom Cruiser although the Olds was dropped after 1992) and convert it to Diesel. That would get 30 MPG on the highway easily even with a stock automatic transmission, but if you stuck a manual transmission in it the car would get even higher. Add a few more mods and you got 36 MPG. However, They have rear-facing seats and I'm not yet sure how they are compared to minivans when it comes to storing a few possessions inside the car with a full load of passengers. With five people in the car the rear seat doesn't need to be up, but with seven I'm wondering about storage capability. (Yeah, Even though I like station wagons I admit that.)
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