Old & Injecting

My overhead instrument cluster odometer it is loosing some mileage as compared to the main odometer. It appears to lose it during the ignition switch off and on transient. If I reset the overhead odometer and the main trip odometer at the same time, they indicate identical mileage until the ignition is turned off. SOMETIMES the overhead odometer indicates a reduced mileage (it is always less mileage) as compared to the main trip odometer when I turn on the ignition. This error also affects the average fuel economy (MPG) and probably the distance to empty (DTE) displays on the overhead console. Any suggestions?