The Stellar Mass-Halo Mass (SMHM) relation provides insight into the galaxy-dark matter halo connection, including information about the central galaxy and cluster’s assembly. In Golden-Marx & Miller (2018), we incorporate the magnitude gap, the difference in brightness between the central and 4th brightest galaxy, into the cluster SMHM relation and observe that at fixed halo mass, clusters with larger magnitude gaps have larger central galaxy stellar masses. This trend is also seen in semi-analytic models, which suggests that it results from the hierarchical assembly of the BCG and galaxy cluster halo. In Golden-Marx & Miller (2019), incorporating the magnitude gap allows us to detect statistically significant late time evolution in the SMHM relation’s slope. Moreover, we identify that the BCG’s outer envelope is more strongly tied to the underlying dark matter halo. Based on comparisons of our results to results from simulations, we suggest that the persistence of the magnitude gap-stellar mass stratification at higher redshifts results from the cluster’s hierarchical assembly. Thus, the magnitude gap may serve as an observational proxy for the cluster’s formation redshift, leading to an observational measure of cluster assembly. Here, we present our latest results on the evolution of the SMHM-magnitude gap relation out to z=0.6 using a combined data set incorporating both SDSS and DES redMaPPer data as well as a comparison to results from the Illustris TNG300 simulation.