You don't have enough choke pretension on the choke. With the truck cold, loosen the 3 screws and turn the choke cover until it closes all the way. Then get in the truck, push the pedal to the floor once, and start the truck. Once it starts, tap the pedal lightly - it should open slightly as it steps to the fast idle position on the cam. As it warms up, it will step along the cam until it is fully open. Also be sure there is no binding of the choke linkage.