[Army]

Don't disregard the advice so far but it sounds to me like an electrical heat related event. When it is cold there is a fault - once the engine is warm - pas de problem (!)

If I were you I'd check and clean all of the relevant electrical contacts - especially those that might get warm. It isn't a bad thing to do anyway - bit of white grease over a cleaned terminal before the winter shows a certain level of motoring dedication...

...I once had a kind of opposite electrical heat related problem with a multi-plug that had fallen too close to an engine => accelerating hard up a hill - suddenly you could only hear the wind! After considerable slowing there was usually a loud pop as the engine started again.