I own a 1997 5.4 liter v8 f150 . I was driving down the highway and it began to vibrate violently. I got a scan tool and found out all the cylinders are misfiring. I replaced the spark plugs, boots, fuel filter, air filter. Then I cleaned the throttle body, Mass air flow sensor, and put injector cleaner in it. I tested the egr valve by opening it while running, results as expected. I also sprayed throttle body cleaner in the intake while running with out the filter. However, once I changed the plugs and boots it has gotten worse,and the gap is correct. I am not sure where to go from here.

 

Check the fuel pressure.