replaced tubes and tires last month, and all of a sudden, having a similar problem, must be the batch of tubes as am having the same problem with both tubes......sometimes have to get to 140lbs of pressure before valve opens...I try to keep mine at 100 lbs psi, so once valve opens, tire is usually at 90 +/-, so I add 10lbs.....no big deal doing this at home with a floor pump, but if I have a roadside issue, getting to 140lb psi with a hand emergency pump will be a challenge...

maybe I should use a little silicon spray on valve?