Old John,

Actually, I did consider that.   I did a Excel spreadsheet that calculates
the fuel cost per mile, given the mpg and cost per gallon.   Printed it out
as a table.

In my area, diesel fuel is going for around 2.20/gal while unleaded regular
is running around 3.75.  So when I'm going down the road at 60, getting 20
mpg from my 4.20/gal diesel fuel, it's costing me 21¢ per mile whereas using
regular gas would be 19¢ per mile.

But, whereas a 6.0L gas engine can probably pull 20 mpg going down the road
at 60, a 454 engine will be hard pressed to get 16 mpg.   I think.  And 16
mpg with $3.75/gal fuel is costing 23¢ per mile.

Saving 2¢ per mile isn't a lot, though.   I drive about 12k miles a year
(mostly solo) which only calculates out to $240. per year in savings.   I've
got about 60k miles on the truck so far, which would work out to around
$1200.    Of course the savings weren't as great when fuel costs were less.
And I've still got a ways to go before I've recouped the greater cost of the
diesel over the gas engine.   But as fuel costs continue to increase, the
savings should also increase.   And I do anticipate that the spread between
the cost of regular gas and diesel fuel should get smaller as the oil
companies react to the trucker's discontent and the rising cost of goods
shipped by truck and rail.

My Mileage Expense Calculator covers fuel costs from $2.25 to $4.50 per
gallon and miles per gallon from 10 to 41.   I will probably need to adjust
it for even higher fuel costs.   Arrrrg!

My Rubicon gets around 16 in town and I can pull 20-22 on the road with
speeds between 55-60.   So it turns out to be my economy car!

Old Ralph