When Finney breaks down crying, his hair is soaked from sweating and exertion. Seconds later when he is on the phone his hair is dry.
When Gwen jumps into the police car with Vance, the number on the rear quarter panel is 440. In the next scene when the car pulls alongside the house, the number is now 426.
When the father of Finney is shown reading The Rocky Mountain News, the paper is printed in broadsheet style. This is incorrect, in 1978, that newspaper was printed in tabloid format.
Finney uses what appears to be an LED flashlight during his captivity. These would not have been available in the late 70s and were not common until the 21st century.
Finns flashlight is obviously an LED, which weren't available until early 2000's.
The movie takes place in 1978, but we see the completed Wells Fargo Center in the opening credits. However, it wasn't fully built until 1983.
The opening scene in 1978 shows a guy at the kid's ballgame opening a can of Coors using a pull tab. In 1978 Coors wasn't using pull tabs but instead used it's own unique two hole push-in style opening system.
In the opening credits a shot of downtown Denver facing west is shown. In the background, to the left of the white high rise, a modern wind turbine is visible. In 1978 there were no wind turbines of this type in Colorado.
When driving through the North Denver neighborhood, one sees a rather large palm tree in a front yard. Not possible climatically in Denver.