I have an 03 GC, and I too have been wanting to get a shorty. While I was at Pep Boys (yea, sometimes you gotta do what ya gotta do) I found a little 4.75 " black stubby from Pilot Automotice, # ANT-029B. The Pep Boys SKU is ANT029B and it was $12.99.
I installed it last night, and I CAN tell a slight difference on AM, but FM is just as clear as ever! It looks great, and it took all of 45 seconds to remove the old antenna, squirt some petroleum jelly into the threads on both the antenna mount and the antenna, and screw it down.
For the money and the look, go for it!