Auto gearbox problems + replacement

[dod]

Hi all,

My 2002 TDi 115 Auto is suffering from gearbox problems - when changing up from 3rd to 4th, and from 4th to 5th, it will make the change then lose drive. The engine revs flare up, but if I take my foot off the throttle and gently nurse it back up I will get some acceleration.

The same thing happens if I put my foot down while in 5th, so overtaking just isn't an option anymore.

I've done a partial fluid change (drain plug removed then new fluid up to level, performed on two different weekends), but no improvement.

Would I be right in assuming it's either the belts slipping in the gearbox, or possibly a crack in something that is stopping the fluid pressure getting high enough to accelerate properly in those gears?

Either way, I'm looking at getting hold of a reconditioned box and swapping them over myself. Any tips on what's required and what to watch out for?

Many thanks!