Not my car so the symptoms are described second hand.
Owner says that today the engine cut out three times. The engine loses power especially when going up hill requiring a change down in gear and higher revs than normal and will sometimes pick back up but sometimes cuts out. The engine will start up again immediately afterwards.
The engine required a new headgasket and skim a couple of months ago and was running well between then and the past few days.
The car is well maintained, including regular oil, filter and plug changes.
Any ideas?