I would guess it is high in nitrogen and that's why it was steamin'. Adding that to the tumbler would've helped break down your "browns", you know the low nitrogen, dried out carbon rich stuff. You probably know this already.

The C:N (Carbon to Nitrogen) ratio of fruit waste ranges from 20:1 to 50:1 which helps explain why fruit will start to rot fairly quickly and is the reason why your 5 gallon bucket of pears generated some heat. That your tumbler composter is not might be because of a too wide C:N ratio, optimal is 30:1, not enough moisture, too much moisture, or insufficient air, or a combination of all of those.

HI Kimmsr
Contents of tumbler , not dry, maybe to wet.
Lots of air through the vents, along with a loose door.
About a month ago I placed about 2 cups of nitrogen pellets...
( I learn quickly) I think...
I'm working at adding much browns now, this hopefully will dry up a little and start it going..

OM will rot wherever it is (assuming there is some moisture content, and not frozen solid) with or without human intervention, which can only speed or delay this process to some extent.