My Series II 380GT is doing exactly this! When driving at speed it will stutter but catch. If it happens when slowing down, it shuts off like i turned the key, but will start. Today it shuddered and gave a CEL and went into limp home mode. Earlier this year (Jan) I had the rocker cover gaskets replaced and injectors and throttle body cleaned and it was fine until recently it started doing it again. It's booked in on Friday, but it is so intermittent and I bet the above codes get mentioned, but I will tell the mechanic about your issue and see what happens too. I HATE intermittent problems.