Most cars lose speed going uphill in higher gears (with the exception of Lizard, which generally gains or maintains speed depending on the gear). For Age or Gnade, you can maintain or increase your speed uphill by shifting gears up and then immediately shifting back down, rhythmically. You want to spend more time in the lower gear than the higher gear, but not much. This technique can also be used on turns to brake without decreasing your speed as much.