Barry - it sounds like your engine management computer was way out of line and you were right to get it re-mapped. As I have said our Plus Six is great in every respect when accelerating, cruising, overtaking etc.
BUT when it comes to stopping then that is another story! The car is presently at the Morgan agents to be worked on until we have better brakes. In their defense I must say that they have loaned us a near new Mazda CX-5 SUV - all the bells and whistles including "self-steering"!
I would most certainly like to hear from other Plus Six owners as to their brakes and even better those who have made real improvements. The number One thing I'm trying to improve is a reduction in brake pedal travel from the 60mm I presently have. Ever other car I have have excellent brakes - the Jaguar E-Pace brakes are almost too severe.