Resonant ultrasound spectroscopy has been used on single-crystal samples to observe pseudoproper ferroelastic softening across the (La,Pr)AlO₃ solid solution. It is suggested that softening is due to the presence of an intrinsic zone-center instability in addition to the small Jahn-Teller stabilization expected for Pr³⁺. Softening increases as smaller Pr³⁺ ions are substituted for larger La³⁺ which is attributed to a simple size effect as well as the possibility of bilinear coupling of the intrinsic instability with the weak Jahn-Teller effect. Superattenuation is observed above 600 K for all samples, which is consistent with twin wall related dissipation behavior seen in other perovskites with octahedral tilting. Superattenuation is also observed in the lowtemperature monoclinic phase, implying a high mobility also for the monoclinic twin walls.