missing and backfire

[69fastback393]

i have a 1995 5.0 ho w/aode in a 78 f100.sitting still it seems to run good from idle to about 3500 rpms and then starts to miss and backfire. its even worse driving it (under load).i changed the plugs today and they were snow white on the tip..any thoughts to what my problem might be?

 

[3greenfords]

I got the same problem and have had for a year. Have not been able to chase it down and I have replaced everything. Take a look under the hood at night and see if there is any arcing from the wires that may be srewing up the timing.