P30 chassis attachments to frame and spark plug wire issues

heat wrap on the steel jackets and on wire if need be and a different brand of plug wire....you say you bought the best....that may be the case in the Borg Warner line....but plug wires will last more than 800 miles

you dont have leaking/warped exhaust gaskets directing exhaust right onto the failed wires do you?

Use the heat wrap on the header tubes...Jegs and Summit and various other retailers sell the heat wrap