Why am I going through Ignition modules?

[Nickelcharlie]

Had to replace my ignition module again in my 86 305 GMC pickup. Why do these go out? I have a friend that owns his own shop and he said when he had a truck like mine he was always replaceing his IM.
I replaced the original distributor and it still does it. I thought I had it fixed by cleaning the contacts on the wires going into the cap but after about a year this ignition module gave it up. These modules are AC Delco! I have had them go out going down the highway and in town driving. This one went out after it started!
Any suggestions how to stop burning these up?