Mac Pro 2008 El Capitan Kernel Loop

Have you checked your RAM?

Long ago, I had on a previous machine one of two chips go bad. This meant frequent kernel panics particularly when using applications that can use suddenly lots of memory like browsers.

The bad news is, back then, TechTools Pro consistently claimed the RAM was fine. A few tech savy recommended I not trust that. I tried the now old but still good "memtest" and it showed immediate failure. TT may be better at detection now.

If that is the case, your RAM may be under warranty--mine was.

I stumbled upon Rember. I will run it tonight and see what I can find out. It’s supposed to have the same programming code as memtest and mentions Memtest in the documentation.
Rember ran through and all RAM was OK. Now, is there a good app to check the Ethernet card? One thing at a time I (we) might get this figured out.
One thing I have noticed is the system prefs need to be rebuilt every other day. I don’t have an El Capitan install disk to do a clean install. Could constant freeze up and shut downs be software?
Breaking news! I found a couple of extensions that a trial VPN service had installed - tap.kext and tun.kext. Apparently they were auto loading something into the ethernet settings on every bootup. I removed these 2 kext files and have been running on Firefox, iTunes, TeamViewer for a couple of hours with no hiccups. Keeping my fingers crossed.