Our 39 Plymouth p2 was running real fast to keep up to 50 mph. I changed the clutch and set up is very important. Changed the oil in the transmisson to Lucas oil. Did the same to the rear end. Gears run a lot quietier and shift smoother also. Engine doesn't rev as much and we run down the highway at around 55 to 60 mph. I'm in Canada so we use kph. That is 85 to 95 kph. Have been putting a lot of mph's this summer, been working Great. Give this a try first, it is the most cost effective way to handle the situation. Our car drives like new and keeps up as well without a lot of stress on the engine. Hope this was helpful. Good Luck George and Louise Johnson P.S. Our car runs so quiet, people don't even know we are behind them most times. I am sending a picture of our car. Never being painted all original inside and out.