The radio station identifies itself as "WCEI - Oklahoma City". A radio station in Oklahoma would begin with a "K" (being west of the Mississippi) River), not a "W", which is for those stations east of it.
McCloud says that they were sprayed with DDT. This episode aired in 1976, DDT was banned in 1972.
The aerial shot of Oklahoma City is the same one used previously for Albuquerque, New Mexico.
When McCloud and Broadhurst stop for gas after arriving in Oklahoma City, they are shown surrounded by a series of moderate hills. Oklahoma City and Oklahoma City County are flat. To get any significant rise in terrain, you have to travel 200 to 250 miles West of Oklahoma City.