Enterprise Resource Planning (ERP) success research is extensive and most approach models to measure the success of its implementation fall short of measuring post-implementation success. Instead of depending on previous frameworks that declare an ERP a failure if framework restrictions are not met, this study suggests a novel methodology for assessing the implementation of any ERP method and its subsequent success via a Group Decision Support System (GDSS). A total of 263 respondents participated online in the research all being employees in local corporate institutions, having interacted with the ERP systems directly, and joined the company before the ERP system went live, making up the study's target group. The study showed improved ERP system success when implemented with organizational culture improvement through GDSS but success was better when combined with access to more IT resources. There was an improvement in Post ERP implementation success (system quality, information quality, organizational impact, workgroup impact, and individual impact) of the organization. Also, implementing ERP without GDSS does not reduce success when it has access to IT resources. For ERP system postimplementation impact, the IT resources capacity of the organization be improved and GDSS engaged to give users opinions.