I have an '02 Supercrew, 5.4L, automatic and my A/C switches from the dash vents to the defroster vents during exceleration while in overdrive. Wheather I'm using the gas pedal or in cruise control above 60 mph. Anyone no whats up? Thanks in advance...

 

This is the normal senario of a vacuum leak issue. You are loosing vaccum in the system and need to check the vacuum lines under the dash, at the control head and also the vacuum cannister under the hood/inner fender for a vacuum leak.