Foaming coolant under heavy load, bad head gasket?

[nkaminar]

Yes, re-torque the head to 55 ft-lb in the morning. As T Marsh said foaming can be caused by a combination of chemicals in the cooling system or just some weird antifreeze. Foaming will not cool the engine. Water and antifreeze conducts heat much better than bubbles. Drain, flush, and fill the cooling system with water. Do a test drive. If it stays within operating temperature, then drain out the water and add 50/50 water and a good brand of antifreeze. T Marsh had good luck with the green Prestone.