99 boxster automatic transmission slipping

[Tomw]

Hi

I have a 1999 boxster 2.5 tiptronic, 86k miles. The transmission recently started slipping after drivng a while and the car has warmed up. It does this in automatic mode, so i then switched to manual tiptronic and it would start doing it also. It finally went into limp home mode with the flashing d/4. The slipping stays in the same gear, it just revs and loses power to the wheels. In other words, it is not jumping gears.
Using the durametric, i got error codes p0733 and p0734.

I changed the transmission fluid and filter, reset the error codes and drove it for a while. It shifted fine for about 15 minutes, then the same slippage problems occurred.

I have searched many forums and seen many ideas, but no clear checklist about how to diagnose on my own. I don't know where to start regarding whether it is the tiptronic module, torque converter, or if the transmission is a goner and needs replacement.

Although i don't relish the idea, i've considered doing the transmission rebuild myself, but i would like to know if i am chasing the correct problem. If the transmission needs rebuilding, any sources on the tech manual to do that?

First though is the diagnosis and how to proceed with that.

Thanks

Tom