The transition of drayage fleets from diesel to battery electric vehicles (BEVs) poses both opportunities and uncertainties, especially regarding long-term economic viability. While total cost of ownership (TCO) is a useful benchmark, fleet operators and investors are equally concerned with investment performance metrics such as payback period and Internal Rate of Return (IRR), which better reflect financial risks and investment return timelines. This study proposes a comprehensive framework to evaluate the economic feasibility of transitioning from diesel to BEVs, jointly analyzing TCO parity conditions, payback periods, and IRRs under different technology, cost, and operational scenarios. Building on a previously developed cost modeling tool, the analysis incorporates evolving battery prices, energy costs, vehicle performance characteristics and other assumptions from 2025 to 2050. Real-world duty cycle data from a Class 8 drayage fleet at the Port of Savannah is used to capture route-level energy demand, vehicle miles traveled (VMT), and the feasibility of adopting BEVs with various battery capacities. The study conducts a multi-dimensional assessment of BEV versus diesel economics, identifying battery cost and electricity price combinations that enable TCO parity, competitive payback periods, and attractive IRRs, while evaluating how these investment thresholds vary across VMT groups, vehicle subpopulations, and evolving technology scenarios. Additionally, the study estimates the evolving share of the fleet that can feasibly electrify over time, highlighting the scale and timing of cost-effective transitions. By explicitly defining electrification investment metrics and integrating high-resolution operational data, this study offers a novel, data-driven approach to inform risk-aware decision-making for fleet electrification and supports actionable planning for energy transition in freight applications.