Well, it sure seems like vacuum trouble to me. Are you certain there is no leak at the intake manifold? It's funny, though, that it would start running fine after some amount of trying, yet stall at a light.
I have experienced a car doing that once and it was the intake air duct that was cracked. It would idle fine in park, but any amount of torque on the engine would open this split and cause the (MAS?) to cause a stalling condition.
In another case, the vacuum hose connector to the brake booster would cause a leak on acceleration/(torque).