I have a 95 Crown Vic LX(not police car). 120K miles. I have a "rumble" in the car while trying to maintain about 35 or 40 mph. It's not at the shift point. It feels like you are running over a rumble strip. If I speed up or slow down it goes away. I have replaced plugs and wires. Maybe the COP? Anybody have any ideas? I hope it's not the tranny. Tranny is full and still a nice red color.