I've experienced nib problems similar to the ones you report, a sort of greasy resistance and occasional skipping, particularly on the downstroke. These are often newness in the nib and will dissapear with use.
Washing the pen through with water will often help and there will probably be instructions about this with the pen.
Sometimes people advise washing new pens through with a weak detergent. Bear in mind though, that some manufacturers discourage this practice, so only do this if you know it won't cause any damage.
The best remedy to this is heavy use.
Incidentally, I find that holding the nib still on the paper for a split second before making the downstroke can often help.
Edited by Ipno Tizer, 06 November 2010 - 19:59.