Okay, firmware was certainly part of the problem. I updated the firmware in the pendant to the latest one for LinuxCNC and it started working much better. Its still not as clean as it is on Windows / Mach machines, but its good.

Then the Tormach "waterproof" mouse started acting glitchy. The first thing I did was clean the mouse and blow off the toolbox liner I use as a mouse pad. The mouse fell apart in my hand. Okay, maybe that was it. I grabbed a brand new USB mouse out of my box of spare parts and the mouse worked perfectly, but the pendant quit.

I took a look at the Tormach mouse, and I could find nothing wrong except for the separation of cover and base plate. Zap-A-Gap CA glue to the rescue... after cleaning all surfaces. Tormach mouse worked great, but pendant was still out.

I rebooted the machine, and the pendant was working again, but the Tormach mouse was glitchy again. I swapped the position of the pendant to the other cluster of USB ports, and rebooted the machine. Mouse works great. Pendant works good. Keyboard glitchy.

Finaly solution was to put the pendant on its own USB bus, and put everything else on the other USB bus. Now everything works decent.

I've never had to do this dance with my Mach 3 machines, and I have four of them currently running this same model pendant. I've had two others that also ran it, but have been retired. Anyway... at the moment everything appears to be working okay. I have pulled the shuttle and tossed it inside the cabinet for now.

Oh, I may also have had one plug on one of the USB buses that was bad. I swapped something from one plug to another at one point and it started working. Who knows. Running a six hour job now.