[tman]

Bonneville, Park Ave, and Lesabre do not share a common chassis. The frame is similar, but not close enough to have interchangable parts. For better performance in the park ave:

Grand touring shocks
Stiffer Sway bars
Upgrade it larger wheels and tires with stiffer sidewalls.

The park ave wasn't exactly designed to be a roadhugging traction machine. Thats what GM has the corvette for...

My park ave handles awesomely for me, going around 35mph onramps to the interstate at 55 is about as far as i can push it, and thats enough for me.