Leonardo,
Congrats on closing in on your build on your S7.
The 200 RPM drop is within the normal drop a person would expect with the ULS....1000 is a crazy number.
Question...when you say you switched the left and right and the problem moved with this change, are you saying that you switched the modules L/R? Or, did you switch something other than, or in addition to, the modules L/R? Thinking some additional info would help with figuring out what the problem is.
Second question...is this a brand new factory ULS; or, is it's history other than new?