Hard start and shutoff

[mustang fanatic]

Hi guy's
In have a 2003 gr cher and this thing just started saturday with the hard start and shutdown. any ideas will be greatly appreciated. I have tried fuel treatment I.E. injector cleaner, I found a tech bulletian that gave a part for repair for the #3 injector it is a heat shield from jeep that is now in place. I think this has helped with the skip when it does start. which is very hard when it is hot. again thanks in advance