I am hoping that it is only the Head Gaskets but here are the symptons.

I have a 1997 JDM ej20K wrx.

Sometimes at about 2000 rpm I will start to lose power and the car will start to shutter and shake. It really slows down and a lot black smoke comes out of the exhaust but once I hit 3000 rpms it will go back to normal.

I have a oil leak around the edges of the block. Also I think I am losing coolant somewhere and don't think it is from the radiator. I have changed out the radiator but sometimes the car will start to over heat. When I check the coolant level in the radiator, I can see I have to add more to it. I have checked for leaks on the radiator but there are none.

What do you guys think it is?

Thanks