More questions about feathering

I have noticed somthing about feathering the Lancair Legacy. When I try to feather the props the plane slows down, is that supposed to happen.
Also, I can't seem to go very fast at high altitudes...
Is this just the Legacy or is that just how planes work?
Also, I can't seem to go very fast at high altitudes...
Is this just the Legacy or is that just how planes work?