Which Toto is it?
The paper could be part of the problem. There is some magic combination of some texture of #2 and Northern paper that was hell on the old 1994 1.6 gpf Gerbers in our home. (Northern paper is comfy, but a known clogger.) The toilets could pack pretty solid so that I had to auger them. I'm using the same paper with Toto EcoDrakes without any problem so far (<knock on porcelain>.) Sometimes it moves a little slow, but it always moves...and disappears. My hope is that 1 year from now I'll report zero plunges from three toilets...but that is a real stretch goal.
Vent or drain problems are possible, particularly in an older home on septic. My Grandparent's farmhouse has always had toilet drain issues and I've never been able to tell which of the weak links was the weakest...the line to the septic routinely had roots in it and the septic tank seemed too small and not well taken care of. Then again I suspected vent issues in other lines. But none of it was in my realm of control.