E 350 6.8 Ltr misfire

I'm new here and this is my problem;

2003 E350 15passenger 6.8 Ltr gasoline V10 160K miles

Symptoms: Hesitation/shudder under mild acceleration, intermittent rough idle. Consistently set code P0309

Plugs were changed at 150K miles so probably not the cause.

Decided to "diagnose" by changing coils as :1 they were the easiest to change and :2 also cheapest.

Started engine and cleared codes. Ran well for first 5 miles of roadtest in normal city traffic until a full throttle acceleration after which the rough running and hesitation returned,

New code P0304 set.

Kinda looks like whatever was causing the problem moved from #9 to #4 ?

I'm anxious to hear any opinions regarding what my next step should be.

If the code is following the coil when you swapped them I'd say it's the coil. Motorcraft #DG-508. I always seem to have a few around.

Thanks for your reply Delta;
I replaced all 10 coils with new ones. The original code showed misfire on #9. Didn't disturb the wiring, injectors or fuel rail but when I was finished a misfire showed up on cyl #4 (code 0304) as soon as I got on it hard about 5 miles into the test run. I'm thinking something may be floating around in the fuel rail but sure would like more information before I start down that road.
Thanks again;
Lliam