The fifth gear chatter is normal. The factory shifter just deadens the sound. Everyone and I mean EVERYONE with a short throw experiences some sort of gear chatter. It's just the nature of the short throw beast. If you want to lessen (but not eliminate) the chatter, try a gasket from CobraBob (do a google search) and get a MGW boot. It will improve by leaps and bounds.
As a matter of fact, I actually worry when I don't hear it. It's a constant reminder that I need to down-shift and floor it!