Denver CO to Gillette Wyo road trip

Sherry and I just got back from our trip to Gillette Wyoming... Gillette is in the North East close to Montana and South Dakota.. we set the Nav to take us from home (Denver) to Gillette.. worked well although there was a ten mile stretch of Hwy 57 leaving Douglas that wasn't a highway on the map.. but the Nav Lady didn't say anything about us driving off in space... we again found the highway on the screen and it was fine... it's about 120 miles from Douglas to Gillette a boring road, but some where about 70 miles out the Nav Lady says, " LEFT TURN 1/4 MILE".... hmmmmm the map doesn't show a turn and we can't find one... the lady doesn't bitch that we didn't turn... the return trip she says the same thing in reverse... at least she's consistent.... we saw one Insight that passed us and waved and two Prii one in a WalMart parking lot but was quicker than we were and poof he was gone.... the other on I-25 about Longmont CO, over took us...had Cal plates waved and like all Californians was in a hurry.. boy, I can sure talk like I'm not a California native.. oh sure, I think we averaged about 50 mpg... drove between 60-75 with a head wind both ways... but we only got gas before leaving Denver and when leaving Gillette... beats the four tanks in the Dakota.. gas at both stops was $1.72... not bad for the Labor Day weekend...
Bob