1989 Blazer firing problems

I have a 1989 Chevy Blazer with what sounds like an ignition problem. It has been in the shop for two weeks, they have determined that while on the scope it randomly will not fire a spark to one cylinder while running. The phenomenon is totally ramdom on which cylinder decides not to fire. The coil, wires, distributor, and other things have been replaced.....Anyone else had this problem? What is the cure????

I Have a 90 Blazer That had the same problem, i took it to the shop....turns out it was the distributer, 89 and 90 actually had a recall on the stock distributers, there is a replacement you can buy for under $100