I think you may have another problem besides a gap issue. I pulled the dealer installed plugs (that I provided since the truck has the URD fuel kit) and found them to be gapped in the low thirties.
But I was not getting an engine check light. Just uneveness.
So in the case of a 3.4, the gap itself did not trigger the light. I would regap to .043 or .044 and also make sure the connections are solid. Regapping to .044 made a dramatic difference in smoothness. Also, like Gadget says, make sure you tighten the little caps on the tops of the plugs.
But I was not getting an engine check light. Just uneveness.
So in the case of a 3.4, the gap itself did not trigger the light. I would regap to .043 or .044 and also make sure the connections are solid. Regapping to .044 made a dramatic difference in smoothness. Also, like Gadget says, make sure you tighten the little caps on the tops of the plugs.