I have an 04 F250 135,000 a "check gauge" light comes on every now and than the oil pressure drops to none than back up to normal, at Idle it also sometimes stays down at nothing or sits at normal. When you are on the gas it sits at the normal level. Oil is full, Thanks

Probably the oil pressure sensor. Get a mechanical guage and check it to be sure. For info on where the oil pressure sensor is, look here...

http://dan.prxy.org/Truck/6L_bible_html/html/Page_025.html