$400 is plain crazy. They charge $100-$125 to install the GT cat-back exhaust on a V-6 in SoCal (and I sure wouldn't expect it to be cheaper here than other places)
Put a set of the Bullitt 17's on about a month ago. The handling is a LOT better than before and I haven't noticed the problem you've mentioned. I only regret waiting so long to make the change.
