4.3L Vortec V6. No "Service Engine Soon" light or OBDC codes. Starts (hot or cold) idles and accelerates normally. But after it's been driven on the highway for several miles on a hot day.... It will have a sporadic miss at idle. (Every second or two) You can feel the miss and see the tach needle dip. I haven't noticed any overly rich smell form the exhaust but I will check that the next time it happens. MPG seems to have dropped a little too. It doesn't stall, even with the A/C on and there is no hesitation during acceleration. The hotter it is outside... The worse the idle miss becomes. Like it's possibly related to the under hood temp. The coolant temp gauge behaves normally. (Does the cooleant temp sensor provide computer input for fuel management?) Rotor, cap, plugs and plug wires were are replaced in January. TPS was replaced last Summer. Without any OBDC codes to go on... I'm guessing. I've heard the coil can act like this when it begins to go bad. Could it be something as simple as the Intake Air Temp sensor? Any other suggestions from the professional mechanics here?