Odd steering feeling

Ok. I'm not going to be off any help but... on some threadless stems if they're not perfectly square to the stem, when you tighten up the top cap it can compress stem onto a part of the headset, causing it to stick slightly. If this is the case trying flipping the stem over, or try a different stem.

Which is of no use to you. But someone else might find it useful.

You should always use a spacer or two, even if very thin ones. It tidies up this interface.
The top cap should only be tightened enough to remove play, then loosened back slightly after stem bolts are done up.

I must say, I've fitted hundreds of Ahead stems and never seen that to be a problem.