Not sure how google figured it but I was not going over any speed limits, just drove consistant with little wasted time at any fuel stops-ate out of an ice chest. Sorry, the 25 hours got me to the Canadian border, not to Great Falls-would have been a couple extra hours. There was a backup at the border that took an hour or so to get past. Had a co-driver but just talked the whole time. The year was 1994. The Milepost is worth hundreds of $ for the info you get, just invaluable info. I drove up from Las Vegas in late Oct, 1992, pulling a 18' trailer. Took 7-8 days, only one driver and tried not to drive after dark due to animals and weather. Late in the fall, the daylight was pretty short and many days were only 300 miles or so.
One tip: You will see little tiny flags on the side of the road that look alot like the flags they mark sprinklers in your yard with. These flags are to mark the frost heaves so they can repair them in the summer. You will learn to spot them and slow down, or you will be hitting the roof with your head. LOL
Second tip: Get gas (top off the tank) every time you can. It can be a long ways between stations; especially near the end of the tourist season. Lots of places just plain lock up and leave when winter shows up.