In addition to all of the above, I would also check for a loose injector wire; very common and produces similar symptoms.
+1 on that one. Also, injector wires are subject to a lot of vibration, so if insufficient service loop is provided between fixed and moving areas (like frame and injector), you can develop a wire break, inside the insulation. This can connect and not connect, intermittently, especially after the area warms up and gets more flexible. I have seen bad crimps on the injector connector(s), that connect most of the time, but again, once everything is warm and flexible, the connection is able to move and intermittently disconnect. This stuff won't throw a code unitl it gets really bad. The ECM can see an open injector wire, and throw a code, but it won't until it has seen an open for some number of cycles in a row.
If your fuel pressure regulator is sticking in the more open position, you could have what you describe. It may have enough fuel pressure to run at low demands, like idle. But, when demand increases, she runs out of juice. Also, while the engine is warming up, the ECM is providing just a bit more injector "on" time (for a richer mix). This could compensate for low fuel rail pressure, until the engine warms up. Your low fuel rail pressure can be due to a sticking pressure regulator. The pump is a constant pressure, but the demand changes, hence the pressure wants to vary. The pressure regulator bypasses all un-needed pressure/fuel back into the tank.
You could have a rub hole in your internal fuel line. Not a crack, but a rub hole, from the fuel line rubbing on the inside of the tank. You will see the rub spot as a place where the line has 2 or 3 small dark spots in a row, on the line ribs. In the early stages, you could get the symptoms you descibe, due to low fuel rail pressure.
Good luck,
Rich P
