Transmission question, 1994 Celica ST Options

[92-gt]

So I went and picked up this car today and I knew before I got there, that there was some transmission issues.

The owner said that it would just pop out of third gear, and I was thinking maybe the linkage was messed up.

Well, when I took it for the test drive, it would go into 3rd gear, but it would just free rev.

When shifting into 4th, it grinds a little bit, and then whines when accelerating.

1st, 2nd, and 5th are all fine as well as reverse.


What do you think could be causing this?

Also, it looks quite easy to replace the transmission on this car, is it?

Thanks in advance!