Shocks for 95 Park Ave

On certain sections of freeway where there is a regular rise and fall of the roadway our 95 Park Ave Ultra sort of bucks along. It's always done this since
we got it in '97. Dealer said the shocks were fine. It now has 96k miles and I'm thinking about changing them. Is there a better shock that would stablize the car a bit without destroying ride comfort, or should I stick with original equipment?
Front, back, both?

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