Did you consider the Fuel Pressure Regulator?

Increasing the fuel pressure in the rails is what it's there for. When the engine, and thus the fuel rails, gets good and hot, there can be a great deal of bubbles forming in the liquid, causing lack of functionality in the injectors. The pressure regulator will increase the pressure the rails are under, decreasing the amount of bubbles that can form in the liquid. Once it cools down, the fuel rails will no longer need the higher pressure, and the fuel pressure regulator will decrease the pressure to the normal function pressure.

All this is controlled by the temperature sensor, I believe that also feeds the ECU, which then activates a VSV, applying vacuum to the pressure regulator, increasing the pressure. The pressure regulator is operated by a diaphragm, which is known to tear, thus no longer functioning. Less common a problem, but still a possibility, is the vacuum line feeding the FPR leaking, and/or the VSV ceasing to function.

Just a few thoughts I got. I get so few any more...
Pat☺