1998 Pontiac Transport chugs when stepping gas

A flashing Check Engine light indicates the most serious conditions and means there's too much raw fuel going into the exhaust system where it's going to overheat and damage the catalytic converter. You're supposed to stop the engine as soon as possible to prevent that. Also, once the light has turned on, there's going to be a diagnostic fault code related to the cause of the problem. The place to start is by having that code read and recorded. Many auto parts stores will do that for you for free.