In this letter, we consider LoRa (Long Range) communications for Internet of Mobile Things (IoMT). When objects move at high speeds, Doppler shifts can cause significant increases in error rates. Previous studies have addressed the Doppler shift problem, but they often suffer from low throughput or high error rates due to noise. This letter proposes a differential frequency-shift chirp modulation (DFSCM) method that overcomes the limitations of existing approaches while demonstrating strong resilience to Doppler shifts, improving communication reliability in high-mobility scenarios. Specifically, the proposed method modulates the frequency difference between the current chirp signal and the previous chirp signal, enabling successful symbol demodulation even in the presence of Doppler shifts. Numerical results demonstrate that the proposed scheme effectively reduces errors caused by noise and Doppler shifts.