Blown Head Gasket Symptoms!

[Vinylspinr]

I know I know about the head gasket symptoms. Changed out the old blown HG with a new HKS metal one and ARP head studs, radiator, cap, water pump, and thermostat. After about an hour of driving, she'll spike up to about 3/4 on the gauge...usually drop shortly after back to normal. Rarely does it stay at 3/4 for more than 5-10 seconds. I do have boil over in the resevoir. I've tested the coolant for exhaust so many times now and still no evidence. I will be getting a slightly higher psi radiator cap and ANOTHER new thermostat but this has been driving me nuts for about 2 years now. Damn near willing to sell it if this doesn't get resolved and I REALLY don't want to do that...have had it for 10 years now.