5 ltr tranz help

i just bought a vq 5ltr stato of an real old bloke, immac condition and after driving it sensably for a couple days suddnly it just loses 3rd, i havnt try'd for forth but i imagen it's gone 2. first and second still work perfectly but when it engages third it just free revs. i've pulld the trans out and was wondering what i need 2 replace and a ruff price if anyone knows. or would it be cheaper 2 get a recon? i dnt get it thoe. i have a friend with the same car with twice the km'z wich has been in numerous burnout comps with no problems? ... althoe i did lend the car 2 my mother and she drove up the hill 2 victor harbor in 4th, could this have caused the problem?