I'm not sure the exact timing, but I think it's since the last update, my saves for large files has slowed to a crawl—several minutes for a 500 MB (raw size) TIF. File export doesn't appear to be effects.
I'm using Photoshop 19.1.1 release on a Mac running MacOS 10.13.3 (High Sierra), saving to an external drive.
I am having the same problem saving Tiff files.
My files are 1GB but I have 32GB Ram. The 1st 95% saves fast but the last 5% can take 5 mins.
Activity monitor shows no other task taking up CPU % (all tasks <10%)
Every now and then the CPU usage for PS spikes to 25-50% in that last 5% of saving the file.
This is very frustrating. Same issue with a newly rebooted system and no other apps running.
The usual answer to this is to disable compression in Preferences > File Handling, but Preferences shows this to be for PSD and PSB files. It can make a massive difference saving times, so I'd be inclined to give a try even if your issue is with TIF files.
Note, we had a similar thread here a few weeks ago, and out of interest and to prove a point, I tried saving a very large file with Compression on and off. A 30 second save with compression off, turned into ten minutes with compression on, and that was with a half reasonable system.