Help! Coolent issue, Coolent preasure?

[1999Gst]

So just finished my 6 bolt swap on my 1999 gst. Got moter from chang's, starts idles perfect! But took for a couple test drives get back and see the top(upper radiator hose) was almost rock hard! Didnt suspect much because i have herd Dsm's have a coolent presure of 13psi. So i removed thermostat to keep cooler anyway. Went for a drive today and on the hiway the Upper radiator hose actually blew off the radiator. I tryed switching radiator cap flushed system refilled with new fluids. So my question is, Am i sappose to have that much preasure? Is my head gasket pushing coolent?(not boosting over 5 psi) Or do i have blockage issue or did i reverse some coolent line? i'll try to get some pics up of my coolent lines etc.. Thanks guys