Tire Valve problems of the 2001 Chevrolet Express

The valve stems on three of my tires were malfunctioning due to improper design of the stems. The problem only occurs at highway speeds. At 70 mph I was loosing as much as 15 psi of air in only 10 miles. The air was leaking around the outside of the valve stems because of their improper design. This problem is very dangerous because there is no indication that it is occuring until the tire(s) goes flat, which, if it occurs at highway speed, could easily result in an accident. I was lucky and saw that my tires were almost flat when I stopped for gas. The improperly designed valve stem has the following lettering on schrader USA tr 600 hp 150.