No, no one has done a block test. But if it was ahead gasket problem, wouldn't I be losing some fluid? I am not losing a drop of fluid, and when I check the fluid it doesn't have any oil mixed with it.

 

you may not lose any coolant, you could have a bad block (Cracked) or a bad head gasket you still may not loose fluid. If a block test doesn't give a good result i would remove the heads and send them out to get fluxed to see if there cracked, and also have them checked for warpage. If they are ok replace your short block I have seen this problem before. Very seldom do you have to replace the block.

 

sounds like possible radiator cap, more likely pressure issue. A clog could explain why the engine is at 250 and the radiator at 150. If you engine hits 250 and your not using synthetic, i highly recommend changing your oil. At 250 is strarts to break down, then you will have another issue too.