99 Silverado 350 missing

OK, here is a good one. I have a 1999 Chevy silverao with a 350 in it. It has that odd looking distributer cap with 4 wires on each side of it where all the odds are on the odd side and evens on the even side.
Anyways. It started mossing a day ago like two cylinders were not fireing.
I disconnected each spark plug wire one at a time at the distributer cap. ALL except 2 ( wires # 3 & 7) would NOT spark across to the wire when it was pulled off the cap. So I figured the wire may be at fault. I switche wores with anothe plug andf the same 3 & 7 still did the same thing telling me it was not th wire. I took the psark plugs out and switched them. Same thing Still 3 & 7. I took 3 & 7 spark plugs out of the cylinders. Ran the engine. They are getting spark.
BUT I am still confused why when all wires are on the plugs that when I pull each wire off the distributer cap why is 3 & 7 not jumping across to the wire like the rest. THis test ussually telles you what cylinders are at fault of missing, whether it be a mecahnical or electrical.
Could 3 & 7, which are right next to each other on the cap be shorting out with each other? And if so would that not cause a backfire?
I'm stumped.
Let me know if you know anything that causes this.
Bobby

I bet your cap is cross-firing. It's a common problem for that design cap. Replace the cap and rotor, and your miss should go missing.

Thank you. I did that the day after and it worked.
Thank you for you time and replt.
Bobby