Don't know how applicable this is, but this has been an issue on Lexus vehicles for years. My GS400 would intermittently do the same thing your CEL does. Even replaced a cat because of it. Turns out, the root issue was faulty post cat O2 sensors. Replaced them, and no problems since.
Try swapping O2 sensor for known good one, or replace with new. Should be cheaper than a new cat.
FYI, I don't own an lgt, YET, but just thought I'd try and help.