Replacing or updating legacy ATE system presents unique challenges to engineers. Some challenges include: alleviating ATE hardware obsolescence, working with limited, or inaccurate design documentation (both hardware and software), and the need to update legacy code and software to more modern applications and languages. Each of these items present their own challenges. But when these issues are combined, this task can be compared to completing a jigsaw puzzle with missing pieces. Addressing one issue will impact the decisions made to resolve other issues. In this paper, we will look at a recent project to replace an obsolete tester for a complex RF system on a major DoD platform with a modern equivalent. The solution uses commercial off-the-shelf hardware from various vendors to replace custom legacy hardware. The original test program, written in FORTRAN, was redeveloped using LabVIEW (TM). We will look at some of the challenges faced and examine the decisions made to meet these challenges. One of the issues we will look at is how the duplication of the legacy communication interface, while allowing for backwards compatibility, increased complexity and integration time. We will examine how external processes and procedures played a role in the decision-making process; and how they contributed to challenges during development and integration. We will show how our standard internal processes resulted in a greater confidence in the decisions made and the understanding gained of the problems. The combined effect drove an examination of decision-making throughout the project. Finally, we will take a look at the final results and suggest improvements to the final product. The goal is not to fault or praise any one individual or group, but to examine the decisions made during the project. We also want to learn from the experience. By creating and utilizing this "lessons learned," we can avoid repeating similar mistakes and make better decisions that can lead to overall better products in the future.