[Randy in ca]

Could it be that the pressure in the tube, when it's out of the tire, is just so much lower than the 40 psi it's at when the tire is inflated? Any idea what pressure is in the tube when inflated outside of the tire? Still pretty low I would guess. Does the tire ever go completely flat if left? Kind of searching here, but all that seems to make sense is that it only leaks at fairly high pressures (?). Strange that 2 different tubes would do the same though. Kinda strange. Good luck.