Folks, I am getting good results by putting 1.75 into UM3 "as is" (no changes to the machine). This is what I am doing:
1. Temperature 215. (this is becuase the feeder has weaker grip on the filament. Make it easy for the feeder)
2. Layer height no more than 0.1mm on 0.4 head. On 0.8 head I allow myself to go higher (up to 0.4). With 0.25 I would not do it at all. (this is because you really want slower feeding). Decreasing print speed also works.
3. Use better filament holder, with thin axis and a silicon lube spray will not hurt. I designed my own: https://www.thingiverse.com/thing:4354166 . This will help the spool roll, further reducing the required feeding force.
4. In CURA, feeding rate set to 265% (which is, of course, diameter ratio squared).
5. Do yourself a favor and watch first 2-3 layers.
6. Same feeder, same PTFE tube, same print cores. No changes to the ultimaker. It just works.
With right settings I have no "feeder slips". However, they might be happening without me noticing, so maybe you should refrain from that from big high-quality prints. But honestly, I am getting perfect results even on fairly complex prints.