I used to reformat the drive and start with a clean install instead of doing an in situ upgrade when each mayor release came out, from the public beta all the way to Mountain Lion (i skipped Lion), but the last six years every update has worked without any hinks so i have become a bit lazier i guess.
Unfortunately, that means you have used the upgrade process for WAY too long. As it is, you could be carrying some "bugs" from, for example, Sierra, which would be 3 upgrades ago.
And what about third party software/compatibility? That is something many folks do not consider, but it is critical.
I should have done it the old way, and by the looks of it it looks like I'm in for a complete reinstall. I might give SuperDuper a shot, thanks for the tip.
You're welcome. However, you current "multi-upgraded" system might contain problematic files. You can use a product like Onyx to help with some of that, along with doing as much disk cleanup as you can. It wold be best, though, to also use a commercial program, like TechTool Pro. I depend upon both of them, and with TechTool Pro, it will most likely not be compatible with Catalina until December or January. But that's OK, as Mojave is just fine.