AWD Transmission: Rebuild transmission / uprated parts

[SynonymForTree]

I've got an 2003 XC90, D5 (d5244t I think) that I've been working through getting it solid.

I've got a core plug oil leak. So I'll be taking the engine out and separating the transmission to sort it.

I haven't had the car long and have only done around 200 miles or so in it, the transmission felt OK but I don't really have much experience driving autos, especially an old one like this.

While it's all out, I'm thinking on whether I should get the transmission reconditioned for peace of mind - from what I know, the auto box is really the weak link of these cars and I don't want to have to get it all back out after I've already done the job once. I have a few questions:

• Has anyone used anyone to rebuild these that they can recommend? What was the cost?
• Is there any sort of uprated parts that can be fitted to make them more reliable?
• Are there any other compatible transmissions that are more reliable?
• Is it worth trying to do it yourself?