Hmmm... well, I finally got around to using ddrescue and it's a little odd.
It hasn't finished yet, but it actually hasn't detected any errors or bad sectors, BUT the speed is now down to ~100 KB/s.
So I'm not sure what's going on with the drive.
It's 500GB.
In the beginning, copying up to 300GB, the speeds are fine.
After 300GB, the speeds plummet. But at least the drive isn't locking up, yet.
I noticed this as well just browsing for files on the drive. When I look at older files they play and copy just fine. When I look at files that have been recently copied onto the drive, they're slow as hell and sometimes lock up the drive.