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We demonstrate rapid, high-fidelity state preparation and measurement in exchange-only Si/SiGe triple-quantum-dot qubits. Fast measurement integration (\\(980\\) ns) and initialization (\\(\\approx 300\\) ns) operations are performed with all-electrical, baseband control. We emphasize a leakage-sensitive joint initialization and measurement metric, developed in the context of exchange-only qubits but applicable more broadly, and report an infidelity of \\(2.5\\pm0.5\\times 10^{-3}\\). This result is enabled by a high-valley-splitting heterostructure, initialization at the 2-to-3 electron charge boundary, and careful assessment and mitigation of \\(T_1\\) during spin-to-charge conversion. The ultimate fidelity is limited by a number of comparably-important factors, and we identify clear paths towards further improved fidelity and speed. Along with an observed single-qubit randomized benchmarking error rate of \\(1.7\\times 10^{-3}\\), this work demonstrates initialization, control, and measurement of Si/SiGe triple-dot qubits at fidelities and durations which are promising for scalable quantum information processing.