sounds like you got yourself a bad valve in #3. depending on where you are located, and your work space, dropping the motor to toss on a replacement head or get a quickie valve job done wouldn't be too hateful imo.
however that being said i'd also see what sort of numbers you get when it's warm. if #3 goes up and gets somewhat more inline with the other readings then i'd be tempted to just leave it alone. more so if this is just a toy and not a main source of transportation. but i'd be staying on top of the valve adjustments to keep an eye on things