What about the fuel pressure regulator, the diaphragm inside could be playing up when it gets hot, as could the fuel pump, 2.2 Vauxhalls are renowned for it, it was even on Watchdog, i know, i flippin had one When it went, it was only apparent when the engine got up to temp, let it cool down and the all was pucker. Have you checked the vacuum line from the fpr isn't pissing out fuel?

As for customers moaning, why do dealers think most customers do all the work themselves?