RUNNING ROUGH BEAUTIFUL hT 4100

My beautiful 1985 Eldorado with a HT4100 IS RUNNING ROUGH. This car has just 22,800 mi.
I put new water pump. it was missing slightely before the water pump change but now rung very rough in drive but when I run in 3 gear at 55 mph it smoothes out. Has anyone any suggestions as to why it runs rough? Please help! Quiltinman


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Not anymore this Beauty is running very smooth like new! After a bout with my Cardiac what evers ..I am back and the rough running has vanished.
Thanks to input from many yesterday I performed the following:
New Custom hi-performance plug wires, Plaitnum plugs, Distributor cap and rotor. New battery and fuel filter.
Going Crusing soon. Thanks Quiltinman

Great looking car, glad with some help here and not a lot of dollars she is running the way she was made to run.
 
Safe cruising.
 
G.A.R.Y.