Thank you for that information and those links Jackal. Now I know where I remembered the high speeds in Montana from!

"Montana technically had no speed limit whatsoever until June 1999, after the Montana legislature met in regular session and enacted a new law. The law's practical effect was to require numeric speed limits on all roads and disallow any speed limit higher than 75 mph (121 km/h)."

(It was too much to copy and paste, but the above quote refers to a period in 1996 through June 1999 when Montana technically had no speed limit. The additional information is in the same article that the quote came from.)