Loss of engine power when driving uphill

There are a number of things that this could be so we need to start with these guides and start crossing them off the list:

https://www.2carpros.com/articles/symptoms-of-low-engine-power

https://youtu.be/U1RoG3I-Oww

Even if something is not the issue, that is good info as it all starts to paint a picture.

Also, do the RPMs go up due to it down shifting but the power is low or does it not downshift at all?

It is unlikely the oil change had anything to do with this but we need to rule it out by checking the oil and make sure it is not low.

Also, is there any hesitation like it is running out of fuel? The fact that this is only happening up hills means it could be a fuel issue.

However, I think you have a torque converter issue but that is harder to prove so let's start with all this info first. Thanks