hard miss under load

Does it do it when its hot? Most fuel pumps that ive experianced going bad often give your 5 liter a "extended crank" on startup. there is a port by your fpr you can hook up a gauge to see what your fuel pressure is. Now the second question: does your car throw a ses light when it misses (check engine light) really before anything I'd check codes first. Ur miss could be caused by even a faulty maf sensor.