New Tundra, Few Questions

It happened again! Twice this weekend. One time I went over a hill in my neighborhood at a relatively low speed of about 20-25mph and it happened (going downhill). I'm feeling stumped.

Since then, I still can't get it to do it with OD off.

What I did this morning was get up to 60ish on the highway (which is about cruising speed around here) and toggle the OD back on so I can cruise at about 2k RPM instead of about 2.5k RPM. No vibrations or anything when I do that.

I'm beginning to think that with OD off (and forgive my ignorance here perhaps), it limits downshifting all the time and locking up the torque converter, in turn keeping steady RPM's around 2k RPM on the driveline and I'm not feeling anything.

Under normal driving with OD on, when it is downshifting or driving around lower RPM's, I feel like something is happening with the driveline causing the "rumble strip" type vibration.

Is this a crazy hypothesis? I am more pointed towards driveline now that it happened at such a low speed in my neighborhood.