OK..this may seem counterintuitive, but something to try. You may have too much weight transfer back to front with 3mm droop rear and 1.5 front. Try reducing rear droop to 2mm,,,Oops, depends on how you are measuring...try reducing the amount of down travel you have in the rear (by screwing the grub screws in), which should reduce the amount of weight transfer to the front...a little droop goes a long way, so make minor changes here, about 1mm at a time.
You might also try sliding the batteries back a little to move some of the battery weight to the rear...
Good luck
Mark