Actually they are doing a better job the higher box sides, like on the F150
an the Silverado, are part of the reason.  Trucks are designed to be trucks,
pretty hard to get a bunch of passengers and cargo into something shaped
like the Pruis that looks like a door stop.

Yeas ago GM and others tried designing streamlined trucks and even
locomotives and railroad cars.   The problem for trucks was the streaming
and extra weight reduced load capacity that offset the economy gained

mike

I've read that the most aerodynamic shape looks more like a banana , with
the ends of the banana pointing downwards.  A truncated back end will create
a low pressure area immediately behind the vehicle and increase drag.

The other area that people often forget about is the undercarriage.  A
shield under the engine compartment will help reduce drag.

Since the 2007 Trunda is not for sale yet, the Silverado probably is "best
in class" for cD.

Bill, I agree that truck manufacturers could be doing things to
improve the aerodynamics of some trucks, but most of those things
would nat make the truck "look" more massive so they get put on the
back burner.

Two comments on your input above:

1) Granted a tear drop is the most aerodynamic shape, but it is blunt
end forward, not pointy end, and the tear drop works so well because
the fluid is constantly being swept toward the back to be replaced by
the next "layer" of fluid. It is a lot like the action of team bicycle
racers. The lead racer peals off to rest in the back while the rest of
the pack forges on.

2) I have always wondered why automotive manufacturers advertize CD
(Coeficient of Drag) rather than D (Drag). In order to compute D for a
vehicle, you multiply CD * Frontal area. It is Drag that your engine
has to push through the wind, not CD. CD is the measure of resistance
per unit area.

That is one of the reasons the exact same car with narrow wide tires
will get better mileage than one with wide tires. The wide tires add
to the frontal area.

Take two cars with the same CD that weigh the same. Drive them at the
same speed over the same course. the one with the smaller frontal area
will get better gas mileage.

Then the article disagrees with commonly available authoritative
data sheets, that (no doubt while lying through their collective
teeth) claim 0.26 -- not a big error but whattheheck. <g>

If so, I suspect Toyota would have installed them.  Overall fuel
efficiency is a selling point on that model.  T would be keen to
improve the Cd wherever possible.

How, exactly, does a pickup with a camper shell look anything like a
teardrop? The teardrop shape has to be fat end first and long thin tail
after to be vaguely aerodynamic (so without the shell would be better if
were going teardrop-analogous). But also
a) We were always taught a teardrop shape isn't the most aerodynamic shape
(urban myth), the rear end of the teardrop is ideal, the front is not. A
standard kiddies fish shape is far better as a teardrop has too much of a
bulbous front. The teardrop is a trade-off of water weight, surface tension
and air resistance all of which are very important at the scale of a drop
but not in the same orders when on the scale of a car.
b)The camper shell helps the situation because it removes the giant
step-down at the rear of the cab which causes turbulence and back-flowing
of the air which creates low pressure behind the cab and attempts to slow
the cab down. As well as creating messy flow after it.
c) the drag co-eff of a car is determined by a lot more than just the
overall body shape, as you mention the wheel arch areas create vast losses
and the underbody is by far the worst and most messy area aerodynamically.
It could be that certain models have a fuel tank in a different place which
aids the flow below the back axle instead of through it all, for example.