I never was able to "fastboot boot" TWRP. I finally gave up and did "fastboot flash recovery <TWRP.img>" Then it would boot from bootloader just fine.
However, I also discovered something odd...If you leave TWRP flashed to recovery, and you power off the handset, then plug it into the charger...It the phone would power itself on and boot to TWRP, only the touch screen would not respond...have to pull battery & unplug to reset...
Reflashed the recovery from the firmware.zip that is inside the 4.2.2 OTA update file, and now there is an on-screen battery meter that works when the handset is charging when powered off.
So, only way I could get TWRP to boot was to flash it to recovery.