The structures presented in this paper demonstrate that large (8′ × 2′ × 1′), lightweight, and strong structures are indeed manufacturable through industrial large scale polymer additive manufacturing. The production experiments done to manufacture these structures resulted in process defects that were identified and documented. Processing failures during manufacturing prompted the modification of several process control parameters (layer height, material choice, bed temperature) and post-processing techniques (annealing). This yielded five specimens, each with a unique treatment modification combination. This paper describes an experimental setup for analyzing the effect of these various processing treatments on large-scale additively manufactured thermoplastic structures. Specifically, it presents and compares the uniaxial compression performance results of ABS chopped fiber composite structures made with different processing treatments. Force-displacement experiments were conducted to determine and compare the effects of such processing modifications on the uniaxial compression performance of the different specimens. The data are also analyzed for transient behavior related to plastic deformation and creep. These data indicate that the large additively manufactured polymer composite structural specimens are stiff and strong in bulk. However, the authors do not draw significant conclusions about the effects of the individual processing treatments themselves. The experimental setup and process of identifying and characterizing significant performance effects of manufacturing modifications are generally useful and applicable to other large scale additively manufactured structural products.