Firstly take it back to the garage and make them aware that the problem still exists.
It still sounds like an electrical fault to me,but ideally the
pressure needs checking on a road test.I know this won't be easy to do,but it would confirm it one way or the other.Until you know if you are actually loosing pressure or not it's going to be guess work and very hit and miss.
It sounds like theres a bad connection somewhere that opens up under hard acceleration,i.e when the engine tips back through the torque reaction of pulling away.
I suppose it's possible that the
may move back in the sump momentarily under the same conditions and let the pump run dry for a second or two,but this is unlikely.
I would suggest that you slightly overfill the
level to see if this makes any difference but you run the risk of damaging the cat if the
gets burnt and goes out through the exhaust so this is a no no!.
I'd give the garage another chance,and see if they can come up with any more ideas.
Sorry I can't be more help but these sort of problems can be a nightmare to fix even if you have the car in front of you!Keep us posted on developments.