Headed for the mountains yesterday and got up to around 220 on some uphills. It didn't used to do this and only seems to be continuing if not getting worse. The added heat seemed to make it ping more too.

I have a new radiator, t-stat, cap, flush and fill, fan clutch and plenum gasket. I've burped it several times but I can still hear the fluid move after most startups. Since it's moving I would assume the pump is fine (unless it is not turning at higher RPMs). The coolant level doesn't seem to be going down.

What else? Anyone blow a head gasket on the 5.9L?
Need some help here. - thanks