If it smells like coolant inside the car do you also have coolant on your floors? I just had a heater core go out on me 2 weeks ago. Windows fogged up one night and my car smelled like hot coolant. I knew right away what it was.
When you replaced the head gaskets did you use the updated OEM ones? Also did you have the heads machined? I did my friends GT 2 months ago and when I was cleaning up the surface of the block I noticed a low spot right by the cylinder and if I didn't have the block resurfaced as well it would've leaked and all of my work would've went to waste.