I have a CalDigit TS3 as well. I can't really explain why (for the same reasons you can't), but I could never get the right combo of cables to get 4K @ 60hz on

I have a CalDigit TS3 as well. I can't really explain why (for the same reasons you can't), but I could never get the right combo of cables to get 4K @ 60hz on 2 27" displays until using the dock-- and I've used a lot of cables, always buying the ones that claim to be the latest displayport/thunderbolt, whatever.