I'm not entirely sure if my car has a transmission filter as I have been unable to find any information related to it.

Yes, that's the connector I'm referring to. Even if it's not dirty, it could still be the source of your problem, and it's way cheaper to replace it then to replace the entire throttle body.
Here's my thread for when I had the same problem:
https://www.matthewsvolvosite.com/forums/viewtopic.php?t ...

I had the exact same problem as you on my s80, and I was convinced my throttle body had failed (even though, as mentioned above, they rarely fail unless there's water damage).

My problem was due to the throttle body connector plug being loose/damaged. The connection between the throttle body and ...

Some Updates
ATF drain & fill has finally been performed. Car is now shifting more smoothly and I have even seen an increase in fuel economy! I will perform another drain & fill in about 10k just as a precaution as this was the first time the ATF had ever been changed in this car (to my knowledge ...

Thanks for your detailed response.
I drain & filled my ATF last week and the car has been driving great.
In comparing old fluid with new, it was extremely dark. I think it was definitely overdue.
I will be performing these drain & fills every 30k as suggested.

Thanks for the input guys.
Someone from another forum mentioned that a 3" downpipe might be overkill and could even be detrimental to performance... is that true?
I'm currently looking at purchasing this cat as the old one is getting pretty old and rusty.
Still looking for a good middle resonator ...

Hahaha thanks Mike, looks like I'll be busy tonight!

6 months later and I still haven't touched my ATF. I haven't had any problems yet, but am I sitting on a time bomb here?

I have some time tonight, so I'm debating on whether I should drain & fill it and maybe mix some of the new fluid with the old fluid as a precuation.

Thoughts?

Been awhile since I posted in my journal!

Stuff that's happened
Currently at 161,000km as of this morning. Finally got around to using a clay bar, car looks great! (at least until winter showed up). Got into a minor accident in December and had to replace some power steering hoses to fix a leak ...

I currently have an exhaust leak. The pipe right after my cat has completely rusted and will need replacing/patching. However, after surveying the exhaust system, it's looking pretty rusty, and I've decided that I might as well take this opportunity to replace and upgrade some exhaust components ...