[speed220mph]

You haven't complained about the pressure plate, so I assume it's ok. The disc is for sure what's giving you problems by giving up from the excessive heat. Organic facings coupled with high torque and a lot of slipping ensures certain failure. I've have excellent success in curing this same problem with ceramic--three puck per side--friction facings. These things love the heat and friction coefficient increases as they get hotter. One thing you've got to watch with this type of disc with mechanical linkages is the loss of free play because the facings get thicker after they are first used. Consequently, you have to readjust your clutch linkage. But if you're using a hydraulic linkage, it will self adjust.