If it's of any consolation, we are all experiencing the same problems:
1) LAN disconnecting
2) USB devices connected to the dock disconnecting
3) External monitors blanking out for a few seconds
4) Fans ramping up and extremely noisy when dock is connected.
It's not the laptop (I replaced 3 for the same reasons you mentioned). It's most likely (or at least I hope so) the thunderbolt software/firmware.
I'm still trying to decide whether to return my TB15 or wait for Intel/Dell to fix this...