To echo what is already said - it seems the only way to go faster there would be to go downhill! There may be some situational environmental conditions that could effect stuff - if it is cold out you might need to open the cylinder cocks to let out condensed water in the pistons, if it is cold you may also check for wheel slip - you may need some sanding action. This is why it tended to be important for engineers and firemen to be used to their locomotives, there's a lot of little things that they'd know or not know from experience about the situation to know why they aren't hitting 30.