Took it down to the shop and after driving the car they are saying it feels like the TCM and it has a 530D code.

not a dealer its a shop that only repairs volvos

Only Volvos of Houston told me its common and its 4th gear. That the 4th gear has worn out. Design flaw from GM. I got a quote of 500 to drop the tranny and replace only 4th. Plus service the tranny.

If I just keep my foot on it and let it go and go it doesn't down shift but as soon as I let off the throttle it down shifts.

OK I just bought this car from the original owner a little old lady who stopped driving it when the transmission light and check engine light came on. It has 84k miles on it. When I first started checking everything out I had 5 codes p0236, p0237 p0732 p0734 and p1816. And note that this car sat for ...