1994 Mercury Cougar 8 cyl

Where is the trouble code hook up located? Will the transmission rapid studdering go away if I change the fluid and filter? It also begins to idle rough after a few minutes while in gear, just replaced a vacuum hose that was leaking, it helped(doesnt stall anymore) seems to be getting better. Any suggestions? Should I paint it yellow with red the red interior? I cant find anyone that ghas done that ! I think I t would loook good. Thanks. Have a nice day