Welcome...we need more info about the bike before saying IF that is NOT normal....at those speeds you are above 5000RPMs and that is usually where the KLR will start to drink fuel and oil if pushed.....watch your oil level!
What has been done to the carb? If nothing and you just or someone just slapped a can on it....what about the airbox, airfilter? Snorkle? Jetting? Engine mods of any kind?
I get above 40 MPG with a fully modded and loaded bike but not at 80mph! 70 yes.....I'm still in the mid 40's easily. No headwind either.