Originally posted by RC51Mike
Page 303 of Roadfood, Copyright 1992: "Frito pie"
Stern's write up on this site says "Fritos" multiple times.
The website of the Cowgirls Hall of Fame Restaurant, however, calls it Frito® Pie.
It really doesn't matter though. If you say Fritos Pie or Frito Pie, you'll be served the same thing, I'm sure.