Officers were called to the westbound carriageway between junctions 15 and 16 around 22.50 GMT on Saturday, 5 November 2022.
The road was closed while investigations were carried out and reopened around 01.30 on Sunday, 6 November 2022.
Enquiries are ongoing into the circumstances and officers are appealing for witnesses.
“Similarly, if you have dash cam footage from the area at the time, please review it and bring anything of significance to our attention.”
Anyone with information should contact Police Scotland on 101 quoting reference 4677 of 5 November 2022.