When Frank takes the train from Chicago to Denver he passes some beautiful scenery, including various desert mesas as well as Glenwood Canyon, both things one would see when approaching Denver via Amtrak from the west, not the east.
When Frank is taken off the plane after his heart attack, he is taken away in an ambulance that said FD NC. While he was scheduled to land in NY, the ambulance was apparently borrowed from another town, probably New Canaan, CT.
When they were first in the limo in Vegas, the car was heading south on LVB, passing the Excalibur on the right. A minute later, the mid-strip hotels were also on the right. This is impossible - unless driving backwards.
During the film, telephone conversations are heard as if coming from the "wires" on the poles next to the track or road. Long distance telephone lines have been buried below ground in cables and later, fiber optic lines, since the 1950s. The wires shown are electric or signaling wires.
The goof item below may give away important plot points.
At the end of the movie when Frank is back home, there is a scene that opens up in the living room, where you see a framed wedding photo on a side table next to an armchair. When Frank goes to place the old Christmas photo he'd intended to give to David on the bookshelf with the other pictures, you can see the wedding photo on the same shelf to the left and when the camera zooms out to the whole room, there is no picture on the side table anymore.