I was driving on freeway about 75 mph when suddenly I felt a difference in gas peddle and heard my engine rev . I realized that I had no 5th gear at that point. I slowed down and shifted down to 4th, I was able to use 4th to get off freeway. I then realized after coming to a stop that I had no gears at all. I can shift into all gears without using clutch but it would not engage them. later found that I do still have 4th gear. I replaced clutch and still no gears.

Its defently internal,if you can put a clutch in then you will have no trouble fixing the gearbox.
when you take the box out have a look at top part of gearbox where the gear leaver fits to,undo plate and take out the gear leaver and first see if the serlecter forks are bent or broken,if theres your problem,but you will still need to strip the rest of the box to make shore there is no other damadge.or get reconditioned box,best of luck

You have an internal transmission damage since you mentioned you only have 4th gear left.