i've got a 4.2 in a e150 it's hard to start at least 3 trimes cranking it befor it starts. it will back fire through intake almost but after it gets started it run fine. now when it's around 48mph or 54mph the motor will buck like it's shuting off. I have replaced the crank shaft acd cam shaft senors could it be the coil pack your the pcm/ecm
any help wound be great tks
Leonard