I was driving down the road yesterday, doing about 80 when my 5th gear slipped out. I can't put the car back into 5th at all. What could be causing this?

 

sounds like your syncro is gone.

 

Synchro

I had the same thing with my car and I also noticed a whirring noise from my tranny in certain gears.

Easiest thing to do is to just replace the tranny, you could have it rebuilt which really isn't that difficult to do yourself but F22 trannys are cheap to come by and it would probably cost about the same if not a bit less.

 

how much are f22 tranny's?

 

I sold mine with engine for $300.

I have seen the tranys by themselves go for around $150 (us) or so and sometimes much less in good working order.