I am new to the site and have a problem with my 2000 4.2 liter. 2 months ago i put new spark plug wires and plugs in my truck, and now it is missing a little bit, only when it is warmed up, and only at low idle or under 2000rpm in any gear (5speed) anyone know what this could be? P.S. just turned over 114,000 miles.. thanks.

 

Could be a loose spark plug, a bad wire (check continuity with multi-meter), or the plug connections in the spark plug boots are getting moisture in them. If you haven't done so already, I recommend you put a dab of silicone grease in each boot to keep the moisture out. Also, check your coil-pack for cracks. That's just my line of thinking from what info I gathered from your post.

 

Did you gap the plugs?