Automatic transmission may produce busy shifting on uphill and downhill. This article analyzes three algorithms about the estimation of road ramp: the first using a longitudinal acceleration, the second using estimated output torque, and the third using the difference between two accelerations. The first method is more accurate than the other two, but it is more expensive because an additional acceleration sensor is needed. The second is more complicated and in some driving conditions, it could not estimate the output torque. The third is based on simple theory and inexpensive since no additional sensor is needed. Some simulation results of avoiding unnecessary gear-shifting are also presented in the paper.