High pressure valve stems

I run 80 PSI in my rear tires and the only problem I have had in over 60K miles has been flats on both rear tires caused by valve stem problems. Both times I was told that it was caused by the stems not being High pressure (these were OEM) ones and the ones they replaced them with were metal. Well today I went to buy four new tires and told them I wanted high pressure valve stems put on. Their reply was that they only had one valve stem that they put on and it was a high pressure one. Since I had already learned that the High pressure stems cost about twice that of the regular stem (and why put a high cost stem on a regular 35 PSI tire), I asked to see the stem. It was a regular all rubber stem. I chose not to get the tires there and left. Now my question to the group is this - is there really an high pressure valve stem that is all rubber? The tires are load range E (10 ply rating). Thanks P.S. And yes I have weighted the vehicle on a cat scale and it needs the