I got hold of "my" computer tech (who is hard to reach), and he told me two things:
1. As mentioned by several of the above posters, the jump-back problem is likely due to keyboard sticking problems. I have another computer, whose keyboard may fit. I'll try switching keyboards, and find out whether it makes a difference.
2. "The slows" is probably due to leftover junk on the disk, with associated problems in the registry. He told me to get the FREE! program CCleaner ("Crap Cleaner") exe and run it to identify what would probably be a huge number of items clogging things up.
I did that, and lo and behold! there were hundreds of items identified. I had CCleaner remove them, and I was told it removed 3440.9MB of "stuff" from the computer!
On my own, I decided that that removal would have left a lot of "orphans" in the registry. As I mentioned in a post above, I had just run Registry Mechanic yesterday, but I ran it again after CCleaner. It identified and fixed 149 registry problems.
I rebooted, and rebooting was much faster than it had been.
After I trade keyboards and run for a while I'll give another report.
In the meantime, thanx to all and sundry for your thoughts and help.