Gearbox problem (yes another one)

[The Monty]

My mum just got home to tell me something is wrong with her car. She sadi when she drove to work this morning it was unusually smooth. Goes to go home this arvo and it sticks in second gear until about 80 k's an hour then wont change unless you back off the accelerator. Then it slams into place with a mighty shove in the back.
Second problem was when changing back into second, or into first, it gives out a loud "zrrrtttt" grindy crunchy noise.
I took it for a drive and verified that this is what is going on. The auto has been fully rebuilt about 24000k's ago, so Im hopung they havent stuffed it in someway.
After we got it done it never felt quite right, almost as if it had 5 gears (weird I know), and when it was taken back, we were told they had never seen the car, blah blah blah (there is a sticker on the windscreen with their name and all that on it).
So whats the go with the forte? Anyone want to shed some light?