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Off the top of my head I can't think of one US based manufacturer that uses anything but DOT 3 (other then maybe Corvettes). Most European based manufacturers from my recollection use DOT 4, due to their potential higher energy dissipation and use of higher metallic pad compounds that would allow for a higher degree of heat transfer to the calipers.
Keep in mind that DOT 4 tends to absorb moisture at a higher rate then DOT 3, and that after about 3 years both fluids end up with similar boiling points if they are not changed out.
And that's the key. SAE studies have shown that the American public does not follow brake fluid maintenance. And based on this fact and that after three years both fluids will be at the same point, in general it does not matter.
Therefore in the OE automotive industry the manufacturers then base their fluid boil tests around this lower point, typically running fluid boil testing at Townes Pass in Death Valley. Although some manufacturers also use other locations.
One of the characteristics of the OE brake pads used one the '99-04 chassis was that it utilized an underlayer (red in color) that acted as a heat barrier to assist in heat resistance. The front pads also used a stainless steel heat shield to protect the caliper boots. Later, the insulators on the back of the pads had two quarter moon projections to take place of the SS shim. Also if you look at the rear calipers you will see heat fins similar to an air cooled engine to assist in brake fluid cooling.
While our brakes in typical driving run rather cool, with aggressive (think Ambulance in cities), larger then stock tires, or mountain passes with trailer brakes not doing their share, the brakes can get over whelmed as these brakes do not have a lot of reserve.
But to your point, IMO YES, "for a truck that is rated to tow 6 or 7 ton trailers down long mountain grades, I would think that a higher boiling point is always a good thing".
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