Some of the posts here are off-topic and really offer nothing of benefit to this thread.
Even though the subject stated "coilpack", there are actually 2 electronic items together, either one of which can have issues?
The complete unit I replaced Sunday was a 25 year old original equipment piece. When I used the Casper's tester for the coils, they all checked good. The problem here was a fault in the electronics of the module unit.
A part like this first generation engine electronic control unit to last that long in a very sever environment under the hood is actually a good record.
The original question has been answered that heat is the major culprit, and a remedy was given to lessen the underhood heat should extend life of the unit. If and when it fails, replacing each unit is not that expensive or difficult.
The basic design and execution of the coilpack as part of the first production vehicle to offer this advanced distributor-less ignition system in 1984 was very good as proven on millions of GM vehicles, and on other makes in later years, and performance wise has been used on many 8 sec. GN's.