irishthump, thanks for that. I think I understand the F1 button, on the Elite its the controller 1 (a dial that is pressed to select).
the locos have definitely been run in on both DC and DCC. From out of the box, B131 ran faster than B125, I put them on a simple loop on the 12 and 6 o'clock positions and one eventually caught up with the other.
I then put in the decoders, same thing, I swapped the decoders, same thing. I think this suggests this is either a mechanism issue or power delivery issue.
Im playing with the CV's at the moment, I've read CV's 2, 3, 4, 5 and 6 on both decoders and they had identical values. I think I have CV5 max speed almost there by reducing the speed of the faster loco. CV 3 acceleration is proving difficult, im down to altering values by units of one, put its still not perfect.
When you say altering CV 54 to 0 may have to be done two or three times, will it have to be reset to its original value and then set it to 0 again?
Again, all the help is much appreciated, not a road i've been down before