The problem occurs at different times. Frequently, at a traffic light, if I shift to neutral and release the clutch while I wait, It can be very hard to shift to first gear when the light changes. While up-shifting through the gears, the effort required varies and can make shifting a real pain in the butt. The gears never grind but I never know how much force will be required to make a shift. Then somtimes it shifts smooth and effortlessly. Does anyone know what causes this to happen?