break-in overheating, Help

[Sammys70]

just searched some old threads but wondering if you guys could come up with other ideas or point me in right direction
heres what i have:
new basic gm crate 350
comp262 cam with 981 springs
duel electric fans
180 themostat that I drilled two small hole in and bench tested !
I manually am turning on fans before I start up!

now trying to break in cam but as I get to 5min or so it overheats
seems like i'm getting flow in radiator
radiator tanks are hot, but I get hold my hand on front of radiator
lower hose is hot but I can touch
top hose is hotter than hell and very firm

I'm leaning towards air trapped in system but feel like I should have got it out by now

gonna try running without thermo tomorrow

any other advice would be nice, I can't wait to drive it!!!