Mr Dennis was 72 and came from Maidenhead.
He died after his silver Volkswagen Golf 5 crashed at the junction 15 flyover of the A74 at about 3.15 pm.
His passenger, a 69-year-old woman, was taken to hospital in a serious condition.
Police are investigating and Constable Lloyd Caven said: “We continue to carry out enquiries into the incident and have spoken to a number of witnesses, however, I would still like to hear from anyone who may have seen the vehicle travelling northbound on the motorway shortly before the collision at junction 15.
“Anyone with any information or who may have footage on their dash cam is asked to contact officers via 101, quoting incident number 2105 of 26 September 2018.”