Actually not, Jerry, for the simple reason that, in general, you won't find
a propane refilling point at every Diesel pump. <G> There's also the reason
that, with their pricing structures, they would have to add double the cost
of the installed system to each [already high-priced] Diesel-engined vehicle
they make.

The issue, here, is that the volume of propane required to support the
large-sized engines comes at the cost of the weight and volume of the tank
required to supply the propane when used continuously.

It's simpler (and cheaper) in the long run to install a slightly more
powerful engine than it is to have to make 2 fuel stops - 1 for the Diesel
and 1 for the propane - when *time* is your enemy.

Propane Injection is better suited to *occasional* use when a bit more power
is needed for a short time [getting up a hill, starting out with a heavy
load] in much the same way as NOx injection on a gasoline-fuelled engine.

The argument over "power enhancements" - chips, injection systems, etc. -
providing "economy enhancements" - lower fuel usage, etc. - is dependent
upon driving style and vehicle usage remaining exactly the same. This, as
I'm sure you know, is most unlikely outside of a "test" environment. ["If
you've got it, flaunt it!"]

Propane Injection Systems *do* deliver what they promise *but* at a
continuing price: you have to give up space for an additional fuel tank that
you'll have to go out of your way to get refilled at inconvenient times
(unless you always stop at Flying-J RV islands for fuel <G>).

For those smaller engines *not* used in OTR trucks - Cummins ISB, Navistar
6L, Isuzu - an electronic solution tailorable to specific requirements can
be applied far more inexpensively *without* the need for the tanks and
plumbing required for a PI System but still provide the same benefits.