Compression in cooling system

[sg4145]

I noticed the temp guage was starting to flucuate on my 2002 7.3L. Checked the coolant level & found it low, also found a crack in the top of the overflow resevoir. Replaced the resevoir today & now I'm getting air pressure building up in my cooling system. I don't find water in the oil & don't think I find any oil in the water, but now it seems to be forcing the pressure out somewhere else, like the upper hose, t-stat housing or water pump. Do I have a blown head gasket? Or a cracked head? HELP!