Suspicious that my problems may be bad RAM I tried to run the memtest program (apparently 'Memtest-86 v 3.2') that I've had on my system for 11 years, haven't used for almost that long. It displays the menu briefly then re-boots.

I found memtest86+, built it, dd-ed it to a USB drive, but it gives me an error about being too big, overlapping the second layer of LILO, or something like that, halts.

Any recommendations for a RAM tester?

I would try SystemRescue and boot it from a flash drive. It has memtest86+

https://www.system-rescue.org/

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Use memtest86+. It's OSS.
https://memtest.org/
v6 is highly recommended for x86_64 systems and required for x86_64 multicore processors to run memory tests with all cores. For ancient ia32 systems older versions may be suitable.

System rescue bootable CDROM, (or on a bootable memstick).
It is always handy to have one or more of these available.

KNOPPIX
The Knoppix system

RESCUETUX
Rescue tools

HIRENS
mini win-xp based. May run when Linux will fail.


They have most every rescue tool, including memory testers, usually multiple ones.

Linux has been known to be a good memory tester itself. It will find memory failures when Windows (win98, winxp) does not notice.
Something about how it uses memory or how much it keeps active in memory instead pushing it to files.

Some older distros had a memtest program on their install CDROM, but it has been awhile since I have seen one.

Thanks. I have this installed on a flash drive in my bucket of parts. I had never used its memtest, forgot it had it. Unfortunately my RAM tested good so my problems must have other causes.