Prelude popping out of 5th

Yeh so my 2001 prelude keeps popping out of 5th gear. I drive 80 miles a day so i pretty much stay in 5th gear, and recently it would start popping out every once in a while and now its so bad it wont stay in 5th but for a second. Every other gear is fine but doing 80 or 85 i need to be in 5th. Does this sound like a clutch prob or a transmission problem? Could it be something to do with manual transmission fluid? Any help is appreciated. Thanks

transmission problem. probably not related to fluid.

well it will stay in for a second and when i see it start to slip out i can push the clutch in and it will go back in...a buddy told me it may be the throwout bearing?

no. if it only happens in one gear most likely its the transmission itself.