You need to get a scanner to see if you have any codes like FICM performance. First thing I would look at is the high pressure oil system. If it is a late 04 (with ICP sensor on the passenger valve cover), check the STC fitting. Could be high pressure oil pump or IPR valve too.
Instead of throwing parts at it, find someone close by with an AutoEnginuity that can check the voltage of the FICM as well as the pressure of the high pressure oil system while cranking. Easy to diagnose/fix if you get the info from AutoEnginuity.