96 Chug-A-Lug or Surge

Since I bought my '96 two years ago (now 65K miles), it's had an engine problem where at highway speeds, either on level road or especially going down a slight hill the engine speed frequently balks or has this swift forward-back-forward-back motion in the car similar to rough idling or engine missing. I spoke to a Caprice owner and he called it Chug-A-Lug and said that the dealer reprograms the engine computer. Indeed, my RM never had this engine program update performed. For $80, the dealer reprogrammed it and now it runs great!

Since I bought my '96 two years ago (now 65K miles), it's had an engine problem where at highway speeds, either on level road or especially going down a slight hill the engine speed frequently balks or has this swift forward-back-forward-back motion in the car similar to rough idling or engine missing. I spoke to a Caprice owner and he called it Chug-A-Lug and said that the dealer reprograms the engine computer. Indeed, my RM never had this engine program update performed. For $80, the dealer reprogrammed it and now it runs great!
Hey, that´s good news. Is there anybody out there who knows what exactly is being reprogrammed? It would be great to know if it´s possible to do with my own ODB-cable and laptop? I have a -95 RMW with ODB-I but the problem should be the same? Is there a "highway mode" in these cars to save gas that needs to be altered (or shutoff) when the engine has gone 30-40K miles or something?