I would 2nd what Ken has just said.
The 6m waterfall has huge drift. I use the OCXO to prevent this.
I can get Zero drift on most TX periods but occasionally. Park mode utilised etc.
It’s as we all know an unpredictable band and also the output power of my 2nd U3S struggles a bit on output power. Very low but perfect to drive the10w linear.
I’m working on the 10w linear to give it a bit more Oomph but even then I’m not expecting any miracles.