2003 Lincoln LS PO353, PO355, PO356

Electrical problem
2003 Lincoln LS 6 cyl 99652 miles

car came in with these codes, replaced #3, #5, #6 coils (NAPA) no better. Checked and thought coil wasn't grounding but in retrospect it may have been too dim for me to see. Sent computer to FL to get fixed and reprogramed no better removed inj. And all were firing while cranking. Fuel pressure was 35lbs and compression was 125lbs on #5 (easiest plug to get to.)It seems like engine runs smooth for about 5 seconds when you first crank it also seems to run smooth when doing KOER test although engine is running about 1600 rpm. Local Ford dealership has car and run all tests to no avail also talked with Ford repair also replaced coils with ford brand no better you can remove coil and plug and ground plug and it fires great. Put it back in hole and it makes no difference in engine performance. Bill