Diffractive beam steering by Digital Micromirror Device enables an efficient way to simultaneously manipulate light both in the spatial and angular domain by spatial and time multiplexing while keeping large area and angular throw product. Long-term stability and susceptibility of beam and image steering rely on how synchronization of ns laser pulse and transition of micromirrors is maintained over time and through variation of device temperature. The long-term performance of the beam steering is evaluated by monitoring diffraction efficiency over 350 hrs. with a 360 Hz repetition rate. Also, diffraction efficiency was monitored while increasing the temperature of the mirror array from 45 to 75 degrees C. Over the period, stable beam steering was observed. A decrease in diffraction efficiency under high temperature was observed. We confirmed readjusting synchronization timing recovered the diffraction efficiency to the level of room temperature. The experimental results show a stable operation of diffractive beam steering by DMD is feasible for the long term, and even under variation of temperature by adaptively adjusting synchronization timing of laser pulse to starting timing of DMD mirror transition.