Along with the things whiteghost has suggested, the PERC system has two settings. One is for low altitutde, one is for high altitude. You can tell which mode your sled is in by the speed that the light blinks (fast or slow.) To change from one mode to the other, hold the PERC button in and the reverse light will change how it blinks. Sometimes going to the opposite mode will allow the reverse feature to work better.