>>>Low revs, 1500-2500, but gentle clutch feathering under gentle acceleration. Think maintaining 5-10 mph after going over a speedbump, or keeping up with stop/go traffic. Slipping the clutch in these circs. causes vibration.<<<
I'll have to try this out....I don't generally hit 2nd/3rd at 5-10 MPH and then slip the clutch. From the manual 1st provides 5.1 MPH per 1000 Rs, 2nd provides 7.7, while 3rd yields 10.7.
So at 5 MPH 1st gear would be at about 1000 RPMs. 2nd would be below idle and 3rd would be way, way below idle RPM.
At 10 MPH 1st would produce about 2000 Rs. 2nd and 3rd would lead to 1300 RPMs / 935 RPMs.
Sounds super low and below where the motor would be comfortable or safe operating when slipping the clutch.
Maybe your exhaust is too loud for the situation? Is it stock?
Once you have just a few MPH the car can be easily driven away in 2nd gear very gently without any drama. But in that case the clutch is all the way out. I sometimes do that if I am rolling in traffic as there is no need to go back to first.