HEI modules run pretty warm and require a heat sink. The stock gm dist. they were originally designed for was thick aluminum that acted as a heat sink. I see where you said you mounted it to either aluminum of stainless steel but weren't sure exactly what. Aluminum makes a good heat sink but I'm not sure aoubt the properties of stainless. Plus you should use some heat sink compound between the module and mounting block to help transfer the heat. Did you do that? If not, maybe it's overheating and shutting down.
