You might check under the hood(carefully) right after start up. You might have a leak at one of the hoses, cold start valve, or injectors. Its a long shot, but you might take a look at your petrol tank. There are two seals at the top, one for pump access and the other for the sender for the gauge. There is an access door under the rear seat to look at the pump one.
It's worth giving the truck a once over on the fuel system. The ethanol they are putting in the fuel these days tends to dry out the rubber. I've had to replace most of the system on our truck already.
regards