I think you can get better mileage from your 84. Tire inflation is the
biggest factor I have found.Check the pressures and adjust them to specs if
needed. My 85 has 39 front and 44 rear. My car tires(on the vanagon) only
go to 44psi , so that is where I put the pressure. Spec on the rear is
48.Many different specs for different vanagons. Also, the timing and O2
sensor need to be good.If you arnt getting a bit of engine surge, these are
most likely ok.A good alignment is supposed to help too.Maybe mobil 1 in
the engine and a synthetic in the trans will help.Waxing that thing may
help too.A bottle of fuel injector cleaner ,or two is a great help too.

I heard that going 1 mph over 55 will be like adding  5 or 10 cents to a
gallon of gas.Last summer and fall , when gas was $3.50 /gallon, I saw most
folks going 75 on the interstate. Add  $ 1.00 or$2.00 to the $3.50, and you
get$4.50 or $5.50 effective/gallon. I heard that americans need to pay
$5.00/gallon to get them to conserve.I believe it.Maybe $6.00.Summer is way
off still, and gas just went up 25 cents in the past week and a
half.$2.60/gallon cheapest in my town.Last summer , and now , and last
year, most everyone passed me on the highway.I think I passed 3 vehicles
all of last year going slower than me:)

I learned 30 or more years ago that driving  fast ,and only going local,
dosent save much time. So I dont often do it. Now ,if you need to go 1000
miles, driving fast is a time saver.Once again, time is money.