I had a carbon seatpost in my old steel frame when I initially brought it, not a fan.
I had issues with my previous titanium frame and the thomson seatpost slipping in that, not sure why it's a thing, but glad there are solutions as the constant readjustment gets annoying after a while.
I've got major problems with alu slipping in Ti too.
Degrease, consider a different seat clamp (the Enigma one I have can do about 7Nm, if greased)
Probably going to switch out for carbon though.