Dynamic characterization of modified single crystal lead magnesium niobate-lead titanate (PMNT) is presented and compared to PMN-28PT and PMN-32PT compositions. Long thin bars with electrodes on the ends were driven in the 33 mode under free conditions to provide large signal material properties. The measurement technique used in this study combines the frequency dependent complex impedance with the measurement of the sample face velocity using a laser vibrometer. This technique characterizes the fundamental half wave length extensional resonance mode of the bar as a function of increased drive amplitude and provides both the linear and non-linear characteristics as a function of increased vibration amplitude, up to material failure. A modified PMNT composition having a Trt up to 125°C was tested. The modified composition showed similar small signal piezoelectric properties to the baseline material. The large signal characteristics also follow the baseline material trends. Therefore, the modified composition provides similar performance with significantly improved temperature stabilityand is a viable candidate for high power sonar transducers.