my 2,5 is doing the exact same thing and she just had a major service with a very reputable l/r garage and all her pressures were/are what they should be and too honest i dont see how keeping the tank full should help especially scince the filter is brand new,
one thing that mine does is all electrics go down completely and you cant even switch the hazards on, and then as if a miricle after a few minutes she turns and then able to drive away, this usually happens within the 1st mile of the journey,
while she was in for her service the gearbox oil was changed,also i have not felt any difference in performance and put the box into sports and booted the hell out of her i felt the gearing going up and then also braked to bring the gears down again,
then when removing the key the msg gearbox fault still appears,
the garage has said i must bring her in and they will run the diagnostics on her,has this brought up any thing when you plugged yours in?
also like normal this always happens at the wrong ****ing time of the month