Help! 99 Tiptronic slipping when warmed up

[engarom]

Ok so i have a weird issue.
I can drive my 99 boxster fine in the morning, as time goes by, maybe 15-20 mins, i start to notice the gear changes getting "loose". the engines revs higher between the shifts.
as i drive more, i can feel the transmission slipping more and more to the point when i go home i could not even climb a very slight incline and it kicked into limp mode.
i parked the car and waited a few hours for it to cool.
wouldnt you know it, i came back out, started it up and climbed the hill no problem.

So, I thought maybe low or bad fluid. I did a full fluid and filter change, drove it around and same problem. Transmission slips more and more the warmer the car gets.

No check engine light, no other issues. As soon as it cools down, it works again.

Anyone seen this or have any idea what is going on?

[78F350]

Check the transmission cooling system. The transmission fluid is cooled by a liquid to liquid cooler mounted on the transmission. There are two valves that operate the cooling. The first one is activated electrically and opens to pass a vacuum to the second valve which opens to let the coolant flow. Maybe one of the valves is stuck? One of the hoses blocked?

[77'911s]

You might check the level first. I know this is not fun if you don't have a lift. If the trans was not serviced in a long time(IE 80-100k), sometimes it takes 2 services to right it. I have to service ours and I'm not looking forward to it.
By the way, what fluid and filter did you use?
Regards

[geetee]

did you fill to correct level at correct temp?
Fill temp is very critical

[NewArt]

When I had my tip, I had to top mine up 3 times driving between each fill to get it right!

[engarom]

I will check the fluid again and check for cooler blockage and let you guys know

[Starter986]

Originally Posted by engarom

I will check the fluid again and check for cooler blockage and let you guys know

And... the... results... were?