In any scene in which Al and driving buddy Pete are shown in the cab of their truck talking, they're sitting right next to each other. However in the long shots of the truck riding down the road, they're right where they would be on opposite ends of the bench seat next to their respective windows.
The narrator of the opening sequences states that Alaska was purchased by "William Seward, President Lincoln's Secretary of State." While Seward had indeed been Lincoln's Secretary of State, Alaska was purchased in 1867, when Seward was the Secretary under President Andrew Johnson.
Mrs. Mason hijacks the truck and forces the driver to speed her away from the scene of her crime, but in all the shots of the truck from the front while it's in motion, only one person - the driver - is visible. Mrs. Mason is clearly not in the truck's cab at all.
The truck that crashes over the mountainside and bursts into flames is an obvious miniature.