We search for evidence of resonant top quark pair production in 955 pb−1 of pp collisions at s√=1.96  TeV recorded with the CDF II detector at the Fermilab Tevatron. For fully reconstructed candidate tt events triggered on leptons with large transverse momentum and containing at least one identified b-quark jet, we compare the invariant mass spectrum of tt pairs to the expected superposition of standard model tt, non-tt backgrounds, and a simple resonance model based on a sequential Z′ boson. We establish upper limits for σ(pp→Z′)⋅Br(Z′→tt) in the Z′ mass interval from 450  GeV/c2 to 900  GeV/c2. A topcolor leptophobic Z′ is ruled out below 720  GeV/c2, and the cross section of any narrow Z′-like state decaying to tt is found to be less than 0.64 pb at 95% C.L. for MZ′ above 700  GeV/c2.