I have 6 Michelin 19.5 tires on my Itasca Suncruiser. New in November 2020. All had been well until the right inside tire went flat while we were on a trip in July of this year. Had a mobile guy out, he tested everything, decided by process of elimination it was probably the valve stem extender. He put a new stainless steel one on, filled it up and we went on our way. It was fine on the way home (about 4 hours). We checked it a couple of more times after we were home and no problems. After that, we didn't check it again for a couple of months, but we did buy TST TPMS for all 6 wheels. My husband put them on last weekend and that same tire was down to 40 PSI! No apparent reason. Filled it up, went on our trip but took our air compressor with us. 2 1/2 hours each way, 4 days of camping and that tire never went below 106 PSI cold and 120 PSI while running. So very strange. What could this be? clearly there is a problem, but I can't fathom what to even tell a tire place!