I had the same issue. Took it to Marc's for some other work and had him pull and clean radiator. It was nasty - even with 18k miles on the car. 1/3 of it was covered in oil from oil cooler lines that had leaked at one time - which attracted all kinds of dust, vegetation, and fuzzy junk. The rest wasn't as bad - but it still had a lot o junk in it. He used like 2 cans of brake clean just to get the oil out (so you know what to expect). If your car doesn't have a debris screen on it you can make one pretty easy.
http://www.zr1.net/forum/showthread.php?t=20178
I also went with Marc's chip - and between the cleaning and the chip I went from running 200 on the road and 230+ in traffic - to about 180 on the road and 210 in traffic...
The shroud takes some wiggling to get off there - I didn't do it but I watched Marc and it takes some careful wiggling and lifting...