Have a 4.3 v8 94 Caprice Classic...At slower speeds it kinda chugs?...surges?...chatters? When someone else drives it they wouldnt even notice it...but it bothers me. You can power thru it, push on the gas and it still has power. About a year ago I gave it sparkplugs, wires, fuel filter and it made very little difference. So what am I looking at? Distributor...Dont know too much about engines...just enough to tell that somethings not quite right of could be a lot better. Acts like it needs a tune up.

 

I had a 1992 Buick Park Avenue that did this... if its the same thing... I was thinking mine was the torque converter going out. However it only did it when in overdrive. Yours may be something else if its doing it in all other gears.

 

Checkout the EGR. valve. They get weak with age. Also the OPTISPARK ignition could be failing due to age or if it has gotten wet inside.

HOPE THIS HELPS