I purchased my 54 last August in the western part of NC. I drove it home to the coast and it ran fine for the most part. The car did develop a small hiccup/misfire/sputter while cruising as I progressed home. The car starts up easy, accelerates like a cat with it's tail on fire, keeps low temps and clean oil. When under a load of acceleration the car runs flawless. As soon as I back off and start cruising along at a speed around 50 there develops a random sputter. It is very subtle but it is driving me nuts because I know how good it can run. I have installed a new HEI Distributor, new plugs, new wires, new grounds, rebuilt the carb, and rewired the entire car throughout the last year. The problem has gotten no better. I was thinking maybe since the car was in the mountain/piedmont region of NC it's entire life maybe it was jetted for elevation. The carb has a #56 Jet in it so I don't know if thats my issue. I do know the heat exchange valve thingy on the manifold is seized open. I doubt that matters but worth mentioning. The only thing I am yet to do is a valve job and replace manifold gaskets....Thanks in advance for any help you can offer guys!