Driving on the interstate this past weekend [I-94] hitting uneven pavement and bumps the front-end was going up and down like a yo-yo. It was very drastic and annoying to say the least. I did just get four new tires and the ride is much smoother than before. They don't look over-inflated but I'm not sure what PSI to set them at (I have the 18" AMG rims with Dunlop SP9000s).

I'm wondering if it is more of a shock or spring or other suspension issue? I have a '99 ML430 with 83K miles--and oem suspension never upgraded or replaced.