We present new limits on resonant tb production in pp collisions at s√=1.96  TeV, using 1.9  fb−1 of data recorded with the CDF II detector at the Fermilab Tevatron. We reconstruct a candidate tb mass in events with a lepton, neutrino candidate, and two or three jets, and search for anomalous tb production as modeled by W′→tb. We set a new limit on a right-handed W′ with standard model-like coupling, excluding any mass below 800  GeV/c2 at 95% C.L. The cross section for any narrow, resonant tb production between 750 and 950  GeV/c2 is found to be less than 0.28 pb at 95% C.L. We also present an exclusion of the W′ coupling strength versus W′ mass over the range 300–950  GeV/c2.