Using the equation for the period of a simple pendulum T=2.pi.sqrt(l/g) where l is the length of the pendulum (let's say, one meter) and g is the acceleration due to gravity (close enough to 9.8 m/s/s), we can see that the period of a one meter long pendulum is 2.00 s. If gravity were (for example) reduced to 5.7 m/s/s the period for the same pendulum would be 2.7 s, which is a longer time. Hence, if gravity is reduced the period increases, which means the pendulum slows down. This is opposite what the effect would suggest.