excessive fuel burn

[Copterdoc]

has anyone had this problem? overnight a 1993 cummins went from 20 mpg to 10. it runs great no smoke. oil is clean. idle is perfect, but when you drive it wants to run at about 80 with very light throttle application. it slows back down and idle perfectly, so it is not a runaway. It is just making tons of power and is running great. it is stack not bombed, but it is like it bombed itself overnight. copterdoc