Okay, so what was the motivation for the cam change?

Those cams are quite a bit different than each other.

Like I said earlier....... cut the oil filter open and see what’s inside.
As much as your car slowed down, if it’s engine related...... it should show up in the filter.

I assume you checked the basic stuff...... timing hasn’t moved.....still getting full throttle, etc.

I’d do a compression and leak down test as well, and if it all looks good..... time to pull the trans pan.