I have the same problem with my Joe Blow pump. The same tube doesn't give me the same problem with a Serfas pump I also have. On all my tubes I always give it the smallest little 'burp' before I pump, but on this tube I MUST let out enough air to get down to 80-90 or it WILL NOT pump up. The same pump on a REI tube on the front wheel never gives me the same issue. I keep thinking I can just change out that problem tube, but laziness seems to stop me. (I also do not want to anger the Tube Gods since this tube has given me no problems for many miles. If I make a non-essential change, I'm afraid I will face Karmic retribution.)