How early should I get to DFW airport?

You should arrive at least 2 hours before your domestic flight departure and 3 hours before if you are traveling internationally.

Is 40 minutes enough time to change planes in DFW?

40 minutes is less time if you want to change planes as it can take time to move from one terminal to another terminal.

2400 Aviation Dr, DFW Airport, TX 75261, USA

Dallas Fort Worth International Airport, address

Distance to the city center of Denver: The airport is located 8 miles northeast of Downtown Denver.