Biphase metallic nanolaminates can exhibit extremely high strengths but suffer losses in strain to failure, and diffuse or "3D" interfaces (3DIs) in Ti/Nb have been shown to improve these properties. In this work, we examine the compositional gradient in the interface and its effect on slip transmission using atom probe tomography (APT) and phase-field dislocation dynamics (PFDD). APT reveals that the 3DI consists of Ti-rich, 50/50, and Nb-rich regions, which we represent in the PFDD model as homogeneous, bilayered, and trilayered interfaces. The critical stress for slip transmission increases with 3DI thickness, while the asymmetry between slip transmission directions decreases with chemical heterogeneity and is minimized for a 5 nm trilayered interface. We propose that the critical stress for slip transfer serves as a proxy for forecasting the effects of 3DIs on mechanical properties, with high transfer stresses linked to higher strengths and reduced asymmetry to higher strains to failure.