Well its been about 8K miles now and my 5.4 has been idling without a stumble. Truck has about 20.5K miles. I don't know if its break in, better gas (I have been using exclusively Chevron), or resetting computer (did this after new air filter at about 13K.

Also exhaust pipe is absolutely clean now. It was very sooty until recently.

Anybody else with same experience?

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'99 f150 S/C 5.4L
Tow package, L/S, 3.55