Getting the same mileage in Diesel vs Gasoline will still cost you more at today's fuel prices.
Apart from that, Fueleconomy.gov shows 19 MPG on the Sienna vs 14 MPG (combined) on a 97 GMC Suburban 2WD (Gasoline). [I can't find the Diesel figures]
Day to day, I would hate to live with a behemoth like the Suburban. I know people are devoted to them, but I could never join that group. The minivan is a perfect conveyance for moving a family around day to day, as it is designed to that purpose. Big sliding doors, easy-access third row, comfort all around, room for people and their stuff.
The Suburban is, first and foremost, a truck. To that end, it's an excellent truck for when you have to also carry people. I rode in one with my family and another (when my family was smaller) while we towed a boat to the lake, and the thing was unflappable. If I had a boat, or a heavy trailer to tow often, I'd get a Suburban, and a small car to drive every other day. (Or at least, every day that I couldn't ride my bike.)
But that's me. Lots of good ideas, here.
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