bolts not surrendering

I can't seem to break the three bolts holding my "spindle hub bearing assembly" free, it's 15mm, I tried a 1/2 in drive "snap on" impact wrench with 400 lbs of torque 90 psi didn't work so i cranked it up to 120 still nothing, heat from hand held propane, now the heads are starting to strip, ohh also pb blast, are my last two options the socket with the spirel, or chisleing the head of the bolt off and easy out the rest? I am at a loss, I'm open to almost any idea,TNT is out of the question sorry guys.
1997 chev k1500