My 1999 F350 6.8L V10 has a slight (and what seems to be intermittant) miss. My code reader (Innova 3100) returns no errors, however. Any ideas on what I can test next? Here is what I've tried so far . . . .

(1) Installed new spark plugs.

• Although the plugs that were removed were that old, I replaced all of the plugs with new ones after properly gapping each per Chilton's manual.

• Fuel pressure with key on and engine off equals 34 psi, which is within the recommended range specefied by Chilton's manual.
• The leak-back <2 psi in 5 minutes (well within spec).
• With engine running, fuel pressure dropped to 28 psi (normal).
• Acquired resistance readings on fuel injectors (all within 11-18 ohm range as specified in Chilton's manual).

(4) With engine running @ ~1500rpm, coils packs unplugged one at a time.

• Each time one of the coil packs was unplugged, there was a noticeable change in engine performance. This led me to conclude that each coil pack and plug was indeed working fine.

I did receive a comment from another shade tree mechanic about a a possible fault in the computer board. But I do not know how to test this, or even where it is located on the vehicle. Any advice here?