Improving Gas Mileage

OK, I would like to see an improvement on Gas Mileage. Now being cars have Computers telling them whatto do, how much air to take in... I don't think Items like TORNADO will work. I have used Amsoil and have noticed an increased in Mileage for the first 2000 miles. ( My mini van was getting 20mpg with Amsoil I got 26 MPG. Highway driving. After the 2000 miles it went down to 21 MPG)
I heard bad things about Slick 50.
My question is, Is there a Product out there That truely Increase MPG that won't cost you a lung. Amsoil I believe is the only product out there but, Geez it is expensive.
Any help would be great.
Vic

Your best bet for improved gas mileage is more air pressure in the tires, but not above the max rating. Also larger tires well help some, but driving technic, in other words, driving with a light foot on the throttle would be your best bet.
There are a few products that will give token improvements in gas mileage, but only that.
I have found one item that mosy likely would give you the best mileage with the least amount or no gas...it's call a SKATE BOARD.