Hey Bruno, those electronic ignition kits like the thunderbolt could actually be your problem. When I was having issues with mine, that was the first thing we put on to try and correct the issue. Then I went through a lot of money fixing other things and ended up figuring out it was those kits that caused the issue. I ended up replacing with a full electronic distributor which completely solved the problem.
I went through all the same things you are going through, coils, fuel, carb rebuilds, and on and on. Took me the right mechanic to figure out it was the darn ignition kit that caused the problem from the beginning. Underway, he was able to watch and determine that the spark was "breaking down" when they got hot. It was so frustrating trying to figure it out, but we got it going now and has never run better.
I can't say for sure, but your problem sounds really similar to what I was going through.
