Are you topping the tank off? There may be some issue with topping the tank off keeping the car from accurately knowing how much gas you had for the tank, so it won't improve your cruise range for future tanks. I've stopped topping off (which is actually bad anyway), and cruise range is fine. But it still takes a little time for the car to learn. I don't think disconnecting anything should be necessary for the car to figure things out as long as you're not overfilling the tank.