1989 Buick Regal Car Surges, Please provide me some input!

I have a 1989 buick regal limited front wheel drive with a 2.8 liter v6 with 69,475 original miles. I love the car and its great on gas. The car has a slight rough idle. However you notice it more when your driving down the highway and let off on the gas, then slightly pressing the accelerator; it then starts surging as if it isn't getting enough gas or that the EGR is wide open. If you press the accelerator down to mid way the car is smooth without hesitation. I've replaced the fuel filter, all three coils, ignition module, air filter, changed oil, put heat in the gas, fuel injector cleaner with clean fuel.

I'm running out of options, can someone help?

Thank you,

Arland