The Big Boy on my bike was completely down last month. Didn't show any movement on the gauge, and aired up fine.
I knew it was low because I could feel a bit of wobble when turning on pavement, but I didn't realize it was below 5.
Just a thought...
Remember these 5.10 Shinko's and Kenda's we are putting on the front are really intended to be rear tires on other bikes. Often much heavier dual sports than the TW.