No Heat

I have a unique problem in a 2000 malibu. Having a problem with the car overheating. It has new head gaskets, lower and upper intake manifold gaskets, and the coolant is not leaking from the anywhere that I can tell. The problem is that after the car runs for about an hour or so, the temperature pegs out. Another problem is that when this happens, the cooling system appears to be overpressurizing, and there is no heat from the heater. Could it be just a bad radiator cap? Another idea I had is the cooling lines going into the heater core are reversed. Would this cause this problem? Any ideas anyone has would be greatly appreciated.

Id check your thermostat.. Sounds like something is plugged up somewhere down the line or there might be air trapped in the system.. Just a guess.

I vote for air in the system. Get a new cap too, Napa has them for $5-$8..

There's an air bleeder screw on the pipe above the water pump.. With the motor cool, fill the overflow tank a bit over the full cold mark, open the bleeder, start the motor, gently squeeze the radiator hoses to force any trapped ari through the system, close bleeder when bubbles stop.

Edit: Turn heater on high too.