Ill chime in on the "vans" I have a 12 ram cargo van and got a 29mpg over 500 mi.
It does have a 6 sp auto and ive done a muffler delete, K&N dropin, 40 psi TP.
I also have used packing tape to block off the upper 4 panels of the front.
I got the mileage to a run to FL from NC. I did have my scangageII onboard and being new to the forum I see I gotta work on inlet air temp as it was only around 20 above outside air temp.
I was guessin the inlet temp was a cause for the decrease in mileage from the summer but from reading on this forum and now ive been reassured of that. thx