A high-performance low-latency transmission system based on a concatenated code consisting of inner four-dimensional five-level pulse-amplitude-modulation (5-PAM) trellis-coded modulation and an outer Reed-Solomon (RS) code is proposed for a high-speed data link over time-dispersive channels. The implementation of high-speed sequence detection in state-of-the-art technology nodes is enabled by a novel reduced state Viterhi detector which includes only one addition in the longest path. The bit-error-rate performance of the proposed transmission scheme for a real-world channel model is evaluated by simulations. Compared with the RS-encoded 4-PAM transmission scheme in the IEEE P802.3bj standard, the proposed transmission system achieves a signal-to-noise ratio advantage of 0.7 dB at a bit error rate of 10(-6) without expanding the bandwidth.