This paper aims to review the consistency of existing GaN stiffness data and measure the high temperature elastic moduli of free-standing (0001) GaN. Dynamic mechanical thermal analysis (DMTA) and impact excitation were used to determine the E33 elastic modulus at room temperature and at temperatures up to 550°C. At room temperature, E33 ranged from 304 GPa to 279 GPa depending on the specific sample and measurement method. Using DMTA and a calibration with silicon, the elastic modulus decreased by 2.17% between 100°C and 500°C, in close agreement with the literature. By testing samples cut at a range of crystal orientations the isotropy of the stiffness in the (0001) plane was confirmed.