cam position sensor

I recently change my head gasket had no problem with starting or going just had oil mix into coolant tank. when i change the head gasket started getting code for cam sensor. I replace the sensor still had the problem i check all wires to and from and timing is right on. it had started ran for while before the code reappeared. The other thing i can think to do is change the exhaust cam so order GM cam and redid the work. I have not finish that yet but question is can aluminum head become polarized to cause the sensor to malfunction?If you can give suggestion i will welcome it of coarse I did have the head shaved and new valves and lifters.