I had the same problem about a year ago and couldn't get my car to run longer than 2 minutes. Changed plugs, wires, dist. and went through 3 Ignition Control Modules. First I had bad Modules then found out that the harness from my MSD 6AL was F@#k-up! Drove me nuts! Oh yeah don't forget to make sure you have a REALLY GOOD GROUND at your Ignition Control Module. After talking with many others on here, they were also having the same problems...

 

Just for future reference 8.5mm wires really aren't necessary for most any of the setups f-bodys run today. They are more of a nuisance than anything especially because they will not fit in the stock location. The best thing to do is to use an 8mm wire. They can still be routed using the stock path so you don't have to worry about them rubbing on any pulley or coming too close to header primaries. Have you zeroed in on the problem cylinder(s)?