97 Sierra with P1351 code

I have a 97 Sierra that will only drive about 100 miles before setting a P0300 which is a random misfire. Occassionally it will set a P1351 which is Ignition control circuit high voltage. This is ussually acompianied with smoke from the tailpipe. It only sets these codes when the truck is idling, the service engine soon light will blink but if I rev the truck to a steady 1500 rpm the light will stop blinking. The truck has a 5.0 305 Vortec V8. Any help will be great.

Does it missfire all of the time and is it noticable? I had a '97 5.7L and it would set the missfire code every morning, it acted like it was running on 4 cyl, untill it reached operating temp then it would run fine. It turned out to be the coolant temp sensor.

It does have a slight miss all of the time. When it sets the code it has a severe miss. I changed the distributor, the cap, rotor, plugs, wires, coil, egr valve but I haven't tried the coolant temp sensor. Like I said there doesn't seem to be any rhyme or reason when it sets a code. I will try the sensor. Thanks

What brand of sparkplugs did you put in the truck?