i had a 421B that used to flame out during fuel stops & going hotter on the plug fixed that too

the V-spec always seems to run best on the OS P3 which is a very hot plug!
i'd still try a fresh plug just to be sure

it sounds like a tuning/plug issue to me

does the engine still have compression when its hot? if its been cooked it will cut out when it gets hot [:'(]

the only other plugs i've used have been Sirio which have the same taper angle & thread length, i'd have to check the exact number though