Ford F-150 - 1997-2003 :: 1998 - Heater Hose Blowing Off

98 F150 2wd 5.4 -even though VIN says its "W" 4.6; it has a 5.4 with 4.6 timing setup-found. But that's a whole other story...

So, Replaced heater core. did the blend door too.

A week later it overheated and blew a heater hose off the core at the firewall (several times). Temp was up and down, forced me into cylinder head protect mode, so i called my mechanic.

Mechanic used a sniffer (blue liquid turns yellow) in my overflow tank and there was exhaust gas in it... so we replaced head gaskets, intake, timing, water pump, radiator and the rotted out rad support.

Got it done and back on the road, but a few weeks later and the heater hose quick disconnect blew off again, spewing coolant all over (again). This was what we thought was part of the original problem- head gasket allowing cylinder compression into the coolant passages. the little rubber hose that comes from the back of the intake and goes up into the heater core builds enough pressure to pop the disconnect right off and I dont know why. Like I said- I thought it was the head gasket blowing pressure into it but that's all been replaced. Why the pressure would be so high at that point, and how do I correct this?

This is my daily driver, so for now I've bypassed the heater core, but I'm afraid that pressure is gonna burst a hose and/or fitting again.