This paper presents a comprehensive analytical framework for evaluating the performance of maximal ratio combining (MRC) diversity systems over Gaussian gain fading channels. The framework is based on a unified moment generating function (MGF) approach, providing a versatile tool for analyzing the diversity gain and outage probability of MRC systems under various fading conditions. By deriving closed-form expressions for the MGF, the framework enables efficient and accurate performance evaluation, facilitating the design and optimization of MRC diversity schemes in practical communication systems.