Magnacor are ultra-high performance wires that have a silicone jacket that insulates REALLY well. The great part is they are relatively inexpensive, at least when you compare the actual cost, since they last hundreds of thousands of miles, vs. factory wires and the like which need replacement every so often.
That said, they are not miracle wires and will still burn through when they make contact with headers, and of course it would be even worse since you'd have to keep buying new individual wires to replace them. You're best off sticking with cheapo wires until you've solved the issue.
Perhaps the heat socks you are using on them are just cosmetic knockoffs and not the good stuff? Maybe the factory rubber/metal insulators would help? I thought the stock wires for the 5.0L Explorer came with some sort of heat protection, but maybe the replacements do not?
Maybe someone with a 5.0L and TMH could be of more help. It might be that you need to get different or custom wires, or just route them a certain way to avoid the issues you've experienced.
