Sputter at high speeds during long drives

There are many things that can cause this issue from a lean mixture, misfire, or a transmission problem. In most cases if it were a misfire the MIL would illuminate. A lean mixture is possible but might make the MIL illuminate also depending upon what is causing the problem. The first thing I would do is to check the EGR valve. A simple test is to disconnect it and drive it under the same conditions to see if it acts up or goes away. If you do disconnect the EGR valve the MIL will illuminate. If that isn't the issue then I would take a data snapshot with a scanner and analyze the data to see what could potentially be the problem.