1990 F150 hard starting
 

1990, 4.9 300 6cyl 4x4 auto : Hard starting. Truck cranks and wants to go, usually after the 4th attempt of cranking it starts. When its at ambient temp, it acts like this. When it is hot, it starts right up, but acts like its loaded down with fuel, coughs and chugs, but then comes out of it after about 15-20 sec and runs smooth. Do I have an injector bleeding by and not holding line pressure? Also, I should add, the previous owner, removed the rear fuel cell & the truck has only the side fuel cell left. I noticed when refueling there is pressure in the tank when unscrewing the cap. Why the pressure?..any input would be much appreciated