Strong PUFs provide low-cost authentication primitive for resource constrained devices. They use inherent process variation as basis to generate a unique fingerprint, which often lacks the required reliability. Environmental factors, and time varying aging mechanisms can further compromise reliability. In this paper, we investigate the impact of power supply voltage and temperature screens to improve strong PUF performance metrics. Our simulation and measurement results in 65 nm show reliability of 97.4% when operating at 0.6V, with 50.1% uniformity and 46.7% uniqueness. A new double arbitration circuit is proposed to assist in detecting unstable challenges. When compared with Majority Voting, the proposed Double Arbiter circuit achieves comparable reliability performance of 99.6% with only half the evaluations.